n:>i):.;lil^1lr■^l^^^|^1l^:lVl;llri1tt!V■l!T:l^■l!1|l!^!ii!t■l^!ili^l;l!■j^l'|;^,^'V.|'.T{§^ ^as B,K^';..v^^ 0. h'-V AGRICULTURAL AND BIOLOGICAL PUBLICATIONS CHARLES V. PIPER, Consulting Editor APPLIED ENTOMOLOGY "OJlllBookChJn raw'-j^iii Dook ksi me, PUBLISHERS OF BOOKS F O R_^ Coal Age ^ Electric Railway Journal Electrical World ^ Engineering News-Record American Machinist v Ingenieria Internacional Engineerings Mining Journal ^ Power Chemical 6 Metallurgical Engineering Electrical Merchandising APPLIED ENTOMOLOGY AN INTRODUCTORY TEXT-BOOK ^>^°)S,. OF INSECTS IN THEIR RELATIONS TO MAN BY H. T. FERNALD, Ph.D. PROFK880R OF ENTOMOLOGY, MASSACHUSETTS ACiRICULTUKAL COLLEGE, AND ENTOMOLOGIST OF THE MASSACHUSETTS AGRICULTURAL EXPERIMENT STATION First Edition McGRAW-HILL BOOK COMPANY, Inc. NEW YORK: 370 SEVENTH AVENUE LONDON: 6 & 8 BOUVERIE ST., E. C. 4 1921 Copyright, 1921, by the McGraw-Hill Book Company, Inc. THE MAP1.R PRKSS TORK; PA to the memory of Professor Charles H. Fernald: the first teacher of Economic Entomology to college students, in this country. PREFACE If one can judge from the answers to about fifty letters of inquiry- sent to teachers of Entomology in colleges in the United States, the teaching of Entomology in this country at the present time is in a rather chaotic condition. Very few of the answers received show much in harmony in subject matter, methods of presentation, or even the line of training the students should receive by a course in the subject. The author believes that in agricultural colleges at least, two distinct groups of students need a knowledge in Entomology, and rather early in their course. One of these groups is composed of students who will never specialize in the subject but need it as part of an agricultural education, and particularly as a tool which they can use wherever insects are related to their special lines of work. They are not particularly interested in such details as the number of antennal segments in insects, the number of branches of the radial vein, or how important a pest on pigweed the insect is: they do not expect to identify insects beyond the order or family at most, relying on specialists available at the State Experiment Stations for such information. But they do desire a general knowledge of the broad outlines of the subject, and a rather complete knowledge of, and if possible, the ability to recognize particularly import- ant insect pests they are liable to meet in the course of their work. The other group consists of those who expect to specialize in the subject, becoming professional entomologists. Their needs will, of course, be different from those of the other group, but an introductory survey such as will meet the requirements of the rest will give the members of this group an excellent foundation for further and more detailed work. The present book is therefore offered as a classroom text for an introductory course in the subject, which shall give a general idea of insects, their structure, life histories and habits, with methods for the control of insect pests in general, followed by a more thorough study of the more important ones found in this country. For use, the writer believes that in few places will all of the text be assigned. Instead, the pests of the country as a whole (treated in large type) and those of the particular region concerned (selected from among those printed in smaller type) would naturally be the parts used in any one place, though the book as a whole should be fairly well applicable to all sections of the country. The author is of the opinion that to avoid too much monotony, it may prove wise to assign Chapters VI to IX inclusive, among those viii PREFACE immediately following. The treatment of the subject matter is such as to permit this. Many of the illustrations included are familiar. Where satisfactory illustrations are already available, it is questionable whether new ones are any gain, particularly when all are new to the student. In this connection the author desires to express his grateful appreciation of the kindness of Dr. W. E. Britton and the Connecticut Experiment Station, and of Prof. J. S. Houser and the Ohio Experiment Station, for the pro- vision of cuts from the publications of those Stations. He is much indebted to Prof. E. D. Sanderson for the use of cuts taken from "Insect Pests of Farm, Garden and Orchard" and from Sanderson and Jackson's "Elementary Entomology," and to the publishers of these books, John Wiley and Sons, Inc., and Ginn and Company respectively, as well as to Dr. E. P. Felt who has kindly allowed the use of reproductions of illus- trations taken from his publications. Dr. J. W. Folsom's kindness and that of his publishers, P. Blakiston's Sons and Company in permitting the use of illustrations from Dr. Folsom's book "Entomology with Reference to its Biological and Economic Aspects," is also much appre- ciated. Ginn and Company have kindly consented to the use of several illustrations from Linville and Kelly's "Textbook in General Zoology," and the side view of the parts of a grasshopper has been obtained by permission of those in charge of the Natural History Survey of Connecti- cut. The largest number of illustrations secured, however, has been obtained through the kind permission of Dr. L. O. Howard of the U. S. Bureau of Entomology to use many which are the property of the Bureau. Photographs from various Experiment Station Reports and Bulletins have also been freely drawn upon. The source from which, each illus- tration has been obtained is indicated in every case. To all the persons and companies above named, I desire to express my thanks. Any book such as this is necessarily a compilation. Probably there are very few if any entomologists in this country who have worked per- sonally on all the insects treated here. The only originality for it which can be claimed therefore, is in the selection of the various topics and their method of presentation. Errors have undoubtedly crept in, and the author will appreciate having his attention called to any which may be found. The author desires to express his appreciation of the aid in the pre- paration of this book given him by his associates. Dr. G. C. Crampton, Dr. W. S. Regan, and Mr. A. I. Bourne, who have gone over various parts of it and have criticized and advised on those which they have examined. Much of any value it may have is due to them, but for any errors and incorrect statements which may be found, the author assumes full responsibility. Amherst, March 1, 1921. H. T. FernaLD. CONTENTS Preface vii CHAPTER 1 Insects and other Animals 1 The larger groups of animals — Their distinctive characters — ^The Arthropoda — Its characters — Animals included — Subdivisions of the group — Their distinctive characters — Tabular statement of the distinctive characters. CHAPTER II The Insect: Its External Structure fi The characters of insects — Number of segments in the embryo — In the adult — The hypodermis — Sutures — Plates — Form of head — Structures on the body — The antenna; — Eyes — Mouthparts — Chewing mouthparts — The thorax — Its appendages— Legs — Wings — The abdomen— Abdominal feet — Ovipositor — Other appendages. CHAPTER III The Insect: Its Internal Structure 15 Digestive organs — Breathing organs — -Circulatory organs — The blood — Excretory organs — Nervous system — Sense organs — Reproductive organs. CHAPTER IV The Development of Insects 2.5 Egg-laying and viviparous insects — ^Description of insect eggs — Hatching — Development of the insect — The Ametabolous development — Hemime- tabolous development — Holometabolous development — Pupation and cocoon making — Transformation of the pupa — Emergence — Common names of Holometabolous larvse. CHAPTER V Losses Caused BY Insects: Nature's Control Methods 32 Amount of the loss not generally realized — Its average amount — To crops — To animals and their products — To forests and their pioducts — To stored materials — By disease — Total loss — Losses increasing — Causes — Intro- duction of foreign insect pests — Reduction in abundance of insectivorous birds — A theoretic state of equilibrium upset by civilization — Nature's methods too slow — Artificial methods necessary. CHAPTER VI Artificial Methods of Control 38 Two groups of methods — Farm practice — Healthy crops — Crop rotation- Plowing — Time of planting — Resistant varieties of plants — Trap crops — Special methods — Hand picking — Repellents — Trap lanterns — Burning — Heat — Miscellaneous methods. X CONTENTS CHAPTER VII Page Insecticides in General: Stomach Poisons 43 Materials classified — ^Conveyance — Dusts — Sprays — Arsenic — Disadvan- tages — Paris green — Disadvantages — Standard formula — ^Variations — Arsenate of lead — Standard formula — Arsenate of lime — Standard formula- Poison baits — Hellebore — Commercial Sodium Fluorid. CHAPTER VIII Contact Insecticides 49 Purposes of contact insecticides — Kerosene emulsion — Miscible oils — Whale-oil soap — Common soap^ — Nicotine — Nicotine sulfate — Lime sulfur wash — Dry sulfur compounds — Sulfur — Pyrethrum, insect powder, or buhach. CHAPTER IX Insecticides and Fungicides: Fumigation 54 Combinations of spray materials — Of insecticides — Of insecticides and fungicides — Injurious combinations — Fumigation — Nature of its action — Limits of availability — Carbon disulfid — Nicotine — Sulfur — Hydrocyanic- acid gas. CHAPTER X The Relationships of Insects 59 Classification — The development of animals in the past — Artificial and natural classifications — ^The original insects — The development of diversity — Resultant groups — Relations of species, genera, families etc. — A sample tree-like classification — Table of classification. CHAPTER XI The Apterygota 62 General structure — Distinctive characters — General description — Divisions of the group — Order Thysanura — Distinctive characters — The Silver Fish — Order Collembola — General features — Distinctive characters — General account. CHAPTER XII The Pterygota. The Ephemerida 65 General considerations on the Pterygota — The Ephemerida — ^General description and structure — Distinctive characters — Life and habits — Importance. CHAPTER XIII The Odonata 68 General description and structure — Distinctive characters — Groups of dragon-flies — Habits — Their life and food — Importance — ^ Abundance. CHAPTER XIV The Plecoptera 72 General description of the group — Distinctive characters — Life and habits — Abundance — Economic importance. CONTENTS xi CHAPTER XV Page The Embiidina 74 General description — Economic importance. CHAPTER XVI The Orthoptera 75 General description — Structure — Division into two sections — The Cursoria — Distinctive characters — Families considered — -The Blattidae — Descrip- tion of Roaches — ^The German Roach — The American Roach — The Aus- tralian Roach — The Oriental Roach or "black beetle" — Control of Roaches — The Mantidse — General considerations — Common Mantids — The Phas- midie — General description of appearance, life history and habits — ^Eco- nomic importance — Control — ^The Saltatoria — -General features — The Acri- did» — Description of grasshoppers — Abundance — Economic importance — Control — Kinds of grasshoppers — Sounds produced — ^Organs of hearing — The Tettigoniidie — General description of the family, habits, life history, etc. — Economic importance — The Gryllida' — General statements — Sounds — Ears — -Economic importance — Kinds of crickets — Tree crickets — Control. CHAPTER XVII The Isoptera 91 The colony — -Its composition — Castes — Stnictures — Distinctive characters — Food — Swarming — Common species — Life and habits — Injuries — ^Control — Zoraptera. CHAPTER XVIII The Dermaptera 95 General description — Distinctive characters — -Importance — Habits — Different species — The European earwig — Injuries — Control. CHAPTER XIX The Coleoptera 98 Structure — Distinctive characters — Life histories and habits — Division into Coleoptera vera and Rhynchophora — Coleoptera vera — Lamp,yridae — Carabidaj — Cicindellidse — Dy tiscidae — Gy rinidse — Hydrophilidae — Staphy- linidae — Silphidse — Dermestidae — Larder beetle — Buffalo Carpet beetle — — Black Carpet beetle — Control — Buprestidse — Flat-headed Apple-tree Borer — Elateridse — Wireworms — control — Scarabaidse — June bugs — Rose chafer — -Japanese Beetle — Chrysomelida; — ^Colorado Potato Beetle — Change of food a possible pest producer — -Striped Cucumber Beetle- — Corn- root Worms — Flea Beetles — Asparagus Beetles — Grape Root Worm — Elm Leaf Beetle — ^Tortoise Beetles — Bruchidse — Pea Weevil — Bean Weevil — . Broad Bean Weevil — Control of Weevils — Cerambycidse — Round-headed Apple-tree Borer — Coccinellida? — Tenebrionidse — Yellow Meal-worm — Meloidse — Rhynchophora — Plum Curculio — Plum Gouger — Cotton Boll Weevil — White Pine Weevil — Alfalfa Weevil — Potato-stalk Weevil — Sweet- potato Weevil — Ipidae — Fruit-tree Bark Beetle. xii CONTENTS CHAPTER XX Page The Strepsiptera 150 General description — Distinctive characters — Habits — Life history — Abun- dance — Importance. CHAPTER XXI The Thysanoptera 153 General features — Structure — Distinctive characters — Habits — Subdivisions — Wheat Thrips — Onion Thrips — Pear Thrips — Citrus Thrips. CHAPTER XXII The Corrodentia 159 General description — Structure — Distinctive characters — Book lice — Psocids — Importance of the group. CHAPTER XXIII The Mallophaga 161 General features — Distinctive characters — Habits — Poultry lice — Control. CHAPTER XXIV The Anoplura .-...• 164 Description — Distinctive characters — Distribution — Life history — Body louse — Relation of lice to disease — ^Crab louse — Lice on domestic animals — Control. CHAPTER XXV The Hemiptera 168 General characters — -Structure of mouthparts — Distinctive characters — Distribution — ^ Habits — Pentatomidse — ^Harlequin Bug — Cydnidse — Coreidae — Squash Bug — Pyrrhocoridte — Cotton Stainer — Lygaiidse — -Chinch Bug — The diseases of Insects — Tingitidaj — Mirida — Meadow Plant Bug — ^Tarn- ished Plant Bug — ^Phymatida? — Reduviida? — Cimicidaj — Bedbug — Gerridre — Notonectidae — Corixidaj — Nepidir — Belostomida>. CUIAPTER XXVI The Homoptera 186 General statements — Distinctive characters — Variations in habits etc. — Honey dew — Classification of the order — Cicadidse — -Periodical Cicada or 17-year Locust — Leaf Hoppers and Tree Hoppers — Apple Leaf hoppers — Rose Leaf hopper — ^Chermidae — Pear Psylla — Aphididse in general — Apple Aphids — -Grape Phylloxera — -Corn Root Aphis — Aleyrodidse — Coccidse in general — -Armored Scales — Oyster-shell Scale — Scurfy Scale — San Jose Scale — ^Rose Scale — Pine Leaf Scale — Purple Scale — Red Scale — Soft Scales — Black Scale — -Terrapin Scale — Cottony Maple Scale — Hemispherical Scale — Mealy Bugs — Citrus Mealy Bug — Long-tailed Mealy Bug — Cottony Cushion Scale— Introduction of enemies of introduced pests. CONTENTS xiii CHAPTER XXVII PAtiB The Neuroptera 221 General features^Distinctive characters — Economic value — Sialidae — Corydalis — Chrysopida! or Aphis lions — Raphidiida) — ^Mantispidai — Myrme- leoni(Ue or Ant lions. CHAPTER XXVIII The Tri(!H()ptkka 22() General description — Distinctive characters — Life and habits — Larval cases — Importance. CHAPTER XXIX The Lepidoptera 230 General features — Structure — Mouthparts — -Distinctive characters — Diver- sity in the order — Life history and development in general — Cossida; — • Leopard Moth — Tineidie — Clothes moths and their control — Codling Moth — ^EgeridiB — Peach Borers — Squash-vine Borer — Gelechiida; — Angoumois Grain Moth — ^Pterophorida; — Pyralida; — Bee Moth — European Corn Borer — Limacodidse — Psychidse — Geometridaj — • Canker worms — Bombycidae — Lasiocampida> — Apple-tree Tent-caterpillar — ^Forest Tent-caterpillar — Ly- mantriida; — Mliite-marked Tussock Moth — Antique or Rusty Tussock Moth— Gypsy Moth— Brown-tail Moth— Notodontidai—Dioptida?— Cali- fornia Oak Worm — Noctuidse in general — ^Cotton Worm — Corn-ear Worm — Army Worm — Fall Army Worm — Cutworms — Arctiida? — Fall Web-worm — Ceratocampida? — Saturniidic — Sphingidje — Tobacco and Tomato Worms — The Butterflies — Hesperiida? — Lycgenidae — ^Danaida; — Nymphalidse — Satyrida? — Pierida; — Imported Cabbage Buttei-fly — Sulfur butterflies — The spreading over the country of introduced insects — Papilionidte — Black Swallow-tail butterfly. CHAPTER XXX The Mecoptbua 300 General features — Distinctive characters — Habits — Food — Importance. CHAPTER XXXI The Diptera 301 General description — Structure — Mouthparts of ailult — Larva> — Pupa? — Distinctive characters — Size and importance of the group — Tipulida;— Culicidte — House Mosquito — Malarial Mosquitoes — Relation to malaria — Yellow Fever Mosquito — Control of mosquitoes— Itonidida; — Clover- flower Midge — ^Hessian Fly — -Wheat Midge — Tabanidse — Simulidje — Asilidse — Syrphida; — ^CEstridse — Ox Warbles — Trypetids — Apple Maggot — Muscidse — House Fly — Its relation to disease — Screw Worm Fly — Sarco- phagida; — Tachinida^ — Tsetse Flies — Anthomyiida; — Cabbage Maggot — Onion Maggot — Pupipara — ^Sheep Tick. CHAPTER XXXII The Siphonaptera 333 General description — Structure — Distinctive characters — Food — Life his- tory and habits — Relation to disease — Control — " Sticktight flea " — Chigue. xiv CONTENTS CHAPTER XXXIII Page The Hymenoptera. 338 General description and structure — Terebrantia and Aculeata — -Develop- ment — Distinctive characters — Importance — Tenthredinoidea — Currant Worm — Pear Slug — Wheat Stem Borers — Horn-tails — Ichneumonoidea — Their importance — Methods of work — Long-tailed Thalessa — Cynipoidea — Gall production — Alternation of generations — Inquilines — -Parasites — Impor- tance of galls — Chalcidoidea — Habits — Wheat Straw Worm — Wheat Joint worm — Clover-seed Chalcis — Fig Blastophaga — Pteromalus puparum — Serphoidea — Long-tailed Pelecinus — Variation in habits of parasitic Hymen- optera — -Chrysidoidea — Sphecoidea — Vespoidea — Progressive development as illustrated by Wasps — Apoidea — Solitary bees — Leaf-cutter bees — Carpenter bees — Bumble bees — Honey bee — Life of a Honey bee colony — Swarming — Value of bee products — Formicoidea — Composition of ant colonies — ^Location of colonies — Swarming — -Establishment of new colonies — Ants and plant lice, etc. — Unusual habits — Argentine Ant — House Ants- Ants in lawns. APPLIED ENTOMOLOGY CHAPTER I INSECTS AND OTHER ANIMALS Among the larger groups of animals now recognized by science, the one known as the Chorda ta is naturally the most familiar, including the mammals, birds, reptiles, fishes, besides numerous forms less well known. Another group,^ also familiar, and called the Mollusca, includes the snails, clam etc., while a third, the Annulata, contains most of the more commonly seen worms. The starfish and sea urchins, often seen at the seashore, belong with other similar animals, to a fourth group called the Echinodermata, and a multitude of tiny beings almost all too small to be seen without the aid of a microscope, are included in the group Protozoa. A sixth large group is composed mainly of soft, jelly-like animals, the more common larger members being called jelly-fish, and to this the name Ccelenterata is applied, and several other groups of less familiar forms are also known. The largest group of all, however, is the Arthropoda, its members found in the seas, in fresh water, on land, or even flying freely; a group with remarkable differences of structure, and so abundant that all the other animals taken together are less than one-sixth as many as the Arthropods. Well-known members of this group are the lobsters, cray- fish and crabs; scorpions, spiders, mites, ticks and "daddy long legs;" the centipedes and millipedes; and last and most abundant of all, the Insects. No one feature will serve to separate the Arthropods from all other animals, but the possession by an animal of several of those here described will enable the observer to determine in each case whether he is examin- ing one of this group. In Arthropods the body is composed of a series of more or less similar pieces or segments, placed one behind another, the line of attachment of these to each other being usually somewhat evident on parts of the body at least. This character is also shown, and indeed more clearly, in some members of the Annulata, such as the common earthworm. Another character of the Arthropods is the presence of jointed legs (or appendages of some kind), as is indicated by the name of the group, and these are not possessed by Annulates. The surface of the body is covered by a secretion which hardens on exposure to the air, 1 APPLIED ENTOMOLOGY forming an outside shell or external skeleton (exo-skeleton), there being practical^ no internal supporting structures except as ingrowths from the outside. In the possession of this external skeleton these animals have a seeming resemblance to the shells (Mollusca), but the materials of which it is composed are quite different, being largely calcium car- bonate in the Mollusca, and chitin which somewhat resembles horn in its nature, sometimes with calcareous salts deposited in it, in the Arthro- poda. In its simplest members the Arthropod body is also practically bilaterally symmetrical, though this condition is concealed somewhat by secondary changes in many of the group. The possession of a bilaterally symmetrical body consisting of a series of segments; an exoskeleton of chitin, and the presence of jointed legs, are then, distinctive features of the Arthropods. To separate the various groups of Arthropods, other characters must be used. Aside from several small sections not often seen, there are five large and important divisions which call for recognition. These are the Crustacea, including the lobster, crab, beach flea, sow bug and many Fig. 1. — Crayfish (Crustacea); about one-half natural size. (Original.) Fig. 2. — "Sow-bug; a crustacean living on land; about natural size. (Original.) Fig. 3 -Millipede (Diplopodn) (From Folsom.) latural size. others; the Diplopoda or Millipedes; the Chilopoda or Centipedes; the Hexapoda or Insects; and the Arachnida, including the scorpions, pseudo- scorpions, spiders, mites, ticks, etc. INSECTS AND OTHER ANIMALS 3 The Crustacea (Fig. 1) are mainly water-inhabiting animals which breathe either by gills, or, in the smaller forms, through the surface of the body. In those cases where its members live on land (Fig. 2) the gills are still present, though in a somewhat modified condition. They have numerous pairs of legs and generally two pairs of antennae (jointed "feelers"). Often some of the body segments are fused with the head to form a cephalothorax. The Diplopoda (Fig. 3) are land animals breathing by air tubes open- ing on the sides of the body and permitting the air to pass in to all the internal parts of the animal. The head bears a pair of antennse and is followed by a series of segments all practically^ alike and each, except Fig. 4. — Centipede {Chilopoda); about three-quarters natural size. (Original.) the first three, with two pairs of legs. The reproductive organs open far forward on the body. In most of the more common members of this group the body is quite cylindrical and when disturbed the animal usually curls up in a sort of close spiral. Small Diplopods about the diameter of the lead of a pencil and gray in color are often found boring into potatoes and roots in the ground in the fall, and are sometimes wrongly called wireworms. The common name "millipede" refers to the large number of legs possessed by these animals. The Chilopoda are also land animals (Fig. 4). Like the Diplopods they have antennse; breathe by air tubes, and the body segments are practically all alike. The general form, however, is rather flattened; each segment bears only one pair of legs, and the reproductive organs open at the hinder end of the body. The front leg on each side is modi- 4 APPLIED ENTOMOLOGY fied to serve as a poison claw. The numerous legs present in these animals has resulted in their receiving the common name "centipede." Fig. 5. — Hairy Spider (Arachnida); about Fig. 6. — Large bodied Spider (Arac^nida); natural size. (Original.) about natural size. (Original.) Fig. 7. — Adult female castor-bean Tick Fig. 8. — Adult female European dog (Arachnida); natural size. (From U. S. Tick (•4rac/?ni(ia); natural size. (From U. S. D. A. Farm. Bull. 1057.) D. A. Farm. Bull. 1057.) Fig. 9. — Grasshopper (Insecta); with wings spread. (From Folsom.) The Arachnida (Figs. 5, 6, 7 and 8) generally have the segments of the body grouped into two sections called the cephalothorax and abdomen. INSECTS AND OTHER ANIMALS 5 No antennae are present and the eight legs are all attached to the first- named section. They breathe either by air tubes somewhat similar to those of the other groups; by sacs containing many thin plates resembling leaves of a book, whence these structures take the name of book-lungs; or, in the smallest forms, directly through the body surface. In the mites there is no evident division of the body into sections. Though most of the group are land forms, a few are aquatic. In the Hexapoda or Insects (Fig. 9) the segments of the body are grouped in three distinct sections; the head, thorax and abdomen. A pair of antennae is (with rare exceptions) present on the head; the six legs are attached to the thorax as are the four wings usually present; the animals breathe by air tubes; and while living under a great diversity of conditions, the group as a whole is emphatically a terrestrial one, though in many cases their early life is spent in water. Distinctive Characters of the Main Arthropod Groups Where found Body divisions \ntennse Legs Breathe by Reproduc- tive organs open Crustacea .... Mainly in water Head and body: often a cepna- lothorax. Two pairs generally Numerous: may be built for swimming Gills or through body surface (rarely by air tubes; Well forward Diplopoda. . . On land Head and body One pair Many: two pairs on most body seg- ments Air tubes Near head Chilopoda • On land Head and body One pair Numerous: one pair on each body segment Air tubes Ne^t to last body seg- ment Arachnida . . . Mainly on land Cephalothorax and abdomen (no divisions in a few cases) None Eight: joined to cephalo- thorax Air tubes, book- lungs or body surface Front part of abdomen (a few ex- ceptions) Hexapoda. . Mainly on land Head, thorax, abdomen One pair Six: joined to thorax Air tubes Near hind end of abdomen CHAPTER n THE mSECT : ITS EXTERN' AI STRUCTURE Biii^iDg together the facts abi'u: insects alrea?. In. riie 'b iatjjL Br Fk. 11. — Froait ^itw oi famd r example, the pordcMis co»- rLei.Ting the segments, is rathex* -li^ht- Spines, hairs, scales or other structures are often ]xesent on the diitin. sometimes entirely concealing its surface and its sutures. The heads erf different ii^ects vary much in form and in the locatMm of the mouth I Fig. 11). In some eases thk is on the undetsde i see Fig. 10), while in others (F%. 12) it is practically on the froot. Heack with ■-j sfaowiag a pro^nAtboos lead. 8 APPLIED ENTOMOLOGY the mouth beneath are called hypognathous : those with it in front are prognathous. Structures found on the head are a pair of antennae, the two compound eyes, ocelH, and the mouth parts. On the thorax are the wings and legs; and on the abdomen are various organs such as the ovipositor, sting, cerci, styli, etc., present in some cases; absent in others. Fig. 13a. — Different forms of insert antennae. iOriainal.) Antennae are nearly always present. They are usually slender, jointed and therefore more or less flexible organs, varying greatly in the number of segments composing them. They are sometimes very short; sometimes long; often thread-like; sometimes enlarged near the tip; in many cases with fine branches either on, one or both sides, so that they resemble feathers or plumes; rarely they fork; in fact are of many forms (Fig. 13). Sense organs are present on them for the sense of touch, and probably also for smell and hearing, at least in some cases. The eyes are of two kinds. There is a pair of com- pound eyes, each of which is a group of similar struc- tures which usually are like tall, slender pyramids in form. Only the bases of these pyramids show on the surface, the remainder being within the head. The bases, closely pressed together, are usually more or less hexagonal, and their outlines can often be easily seen with a magnifying glass. They are called facets, and the eyes themselves are sometimes termed the facetted eyes. The other kind of eyes, called ocelli, may be absent, or if present, may vary in number in different insects, three being perhaps the most usual. Each, as seen from the surface, is a nearly circular, convex spot about the size of one of the facets of a compound eye. It may be larger than this, but is never equal to an entire compound eye in size. In some cases a cluster of ocelli or of the pyramids of the compound eyes is found, not closely pressed together Fig. 136. — An- tennae of Cecropia Moth. (Samia ce- cropia L.) About twice natural size. (Original.) THE INSECT: ITS EXTERNAL STRUCTURE 9 but somewhat separated, and such groups are called agglomerate eyes. The chitin of the surface of the body is transparent where it covers the surface of an eye, permitting access of light to the sensory struc- tures within: elsewhere it is usually pigmented and rather opaque. The mouth parts of insects vary extremely in their structure. Appar- ently the original mouth parts were for biting and chewing, and this type is very common. In some groups, however, they have been trans- formed into a sucking apparatus. Biting mouth pails, being the more Fig. 14. -Three types of insect mandibles, greatly enlarged. Somewhat diagrammatic. (Original.) primitive and simple, are described here, while sucking mouth parts having been differently transformed in different groups will be taken up in connection with those groups. In front of (in hypognathous heads), or above the mouth opening (prognathous heads) is the front lip or labrum. It is a thin flap, hinged to the skeleton of the head and moves forward and backward. It is often more or less divided by a central notch at the middle of its free edge. Its inner surface, form- ing the roof of the mouth, is often called the epipharynx. At the sides of the mouth open- ing, immediately behind the lab- rum, is a pair of jaws, the mandibles. These differ greatly in form in different insects (Fig. 14). They are often stout, heavy structures with crushing faces bearing blunt proj ections or teeth ; sometimes they are long, curved and rather slender. In general their form is adapted to the feeding habits of the insect. Immediately behind each mandible at the side of the mouth is a second appendage, the maxilla. This differs markedly from the mandible, being much weaker, and composed of a number of pieces (Fig. 15). The tips and outer internal margins of the maxillae usually bear numerous Fig. 15. — Two types of insect maxilla greatly enlarged. Somewhat diagrammatic. (Original.) 10 APPLIED ENTOMOLOGY spines or hairs, but this condition varies according to the nature of the food of the insect. Attached on the outer side of each maxilla not far from where the latter articulates with the head, is a sort of tiny antenna- like structure consisting of from one to six (usually five) segments, which is called the maxillary palpus. The function of the maxillae appears to be to hold and retain the food in the mouth while it is being worked upon by the mandibles, and also to aid these in breaking it up. The presence of sense organs on the maxillary palpi suggests that these are possibly concerned with the sense of smell. Both mandibles and maxillae move sideways. Fig. 16. — Two types of insect labium much enlarged. Somewhat diagrammatic. (Original.) Behind the maxillae and closing the mouth opening behind, is the hinder lip or labium (Fig. 16). This was evidently once a pair of jaws somewhat similar to the maxillae, but with no mouth cavity between to separate them, their inner edges have grown together to varying degrees in different insects. In some, only one or two of the pieces nearest the head have fused: in others, fusion all the way to the tip has been accomplished, and all intermediate stages also occur, thus producing a structure which now moves forward and backward like the front lip, but which may be complete, partially, or almost entirely cleft in the middle line. Like the maxilla the labium has a palpus on each side arising from near its base, and composed of three (rarely four) segments. The func- tion of these labial palpi appears to be similar to that of the maxillary palpi. Near the base of the labium on its inner or mouth side there is fre- quently a fleshy swelling more or less covered by bristles or hairs, which is called the hypopharynx, lingua or tongue. It varies greatly in size and form. The thorax has its three segments usually quite clearly marked. Each segment bears a pair of legs, but the prothorax, or first of the three behind the head, bears no wings. On the second or mesothorax, and on the third or metathorax, both wings and legs occur in the majority THE INSECT: ITS EXTERNAL STRUCTURE 11 of insects. There is a tendency in some groups, carried farthest in the higher Hymenoptera, for the first segment of the abdomen to consohdate more closely with the metathorax than with the second abdominal seg- FiG. 17. — Different forms of insect legs. A, Cicindela sexyultata Fab. (beetle) ; B, Nemohius fascialus De G. (cricket) hind leg; C, Stagomantis Carolina L. (Mantis) fore leg; D, Pelocoris fnnoralus P. B. (carnivorous bug) fore leg; E, GryUotalpa borcalis Burm. (mole cricket) fore leg; F. Canthon IcBvis Dru. (a digging beetle) fore leg; G, Phanceus carnifex L. (a digging beetle) fore tibia and tarsus of female; H, same, fore tibia of male; /, Dytiscus fasciventria Say, male (water beetle) fore leg; C, coxa; /, femur; s, spine; t, trochanter; tb, tibia; internal structures of insects are of any fi;reat importance from the standpoint of control methods, but some knowledge of them and their arrangement is desirable. Digestive Organs (Fig. 22). — The alimentary canal extends from the mouth through about the center of the body to the anus at the hinder end. In those insects whose food is most concentrated (Fig. 23), it is in its simplest form and is but little if any longer than the body. In those which feed on less concentrated food (Fig. 24), the necessity for a greater digestive and absorptive surface has resulted in an increase of its length and the accommodation of this within the body by the production of loops and coils. Fig. 22. — Diagrammatic longitudinal section of an insect to show the arrangement of the internal organs. {After Berlese.) In the embryo the alimentary canal forms as three separate sections which connect later. One of these is an ingrowth from the surface where the mouth is to be; another and similar ingrowth occurs where the anus fonns; and a third forming earlier than the other two, arises as two masses of cells, one near each end of the embryo, wliich move inward and toward each other, unite, and surround the yolk. Later, when this has been absorbed, a space is left with which the two ingrowths already mentioned connect, the hollow centers of all three joining to form the tube through which the food travels. The ingrowth from the mouth is usually called the fore-intestine, the central portion the mid-intestine, and the ingrowth from the anus the hind-intestine. The first and last 15 16 APPLIED ENTOMOLOGY of these begin to grow inward from the surface of the body after that surface has begun the formation of its chitinous exo-skeleton, and accordingly also have this power, and line the inside of the parts of the canal which they form, with chitin. In that portion of the canal termed the mid-intestine, however, this power does not appear to be present, and the mid-intestine is without this lining. V \ v| / v_ 1 #^ ^ %oe i ft) "I Kpv cii W \l "'" vm \ w ^ ¥ P ai ^^ r "- ^ ^ r^ V aa ^ ^ { Fig. 23. — Alimentary canal of a Carnivorous Beetle, ad, anal glands; cd, stomach; id, hind intestine; in, crop; A', head and mouth parts; ce, oesophagus; pv, proventriculus; r, rectum; vm, malpighian tul)es. {Modified from Lang'n Lchrbiich.) The mid-intestine forms the stomach of the adult insect; the fore-intestine forms those parts of the alimentary canal from the mouth to the stomach; and the hind-intestine those from the stomach to the anus.. Each of these sections may sometimes have portions differing in structure, producing a greater or lesser number of subdivisions. Thus the fore-intestine, by differences of structure, may sometimes con- sist of a mouth cavity, oesophagus, crop and proventriculus: the stomach may develop side pouches or gastric caeca; and the hind-intestine is often separable by differences of structure into an ileum, colon and rectum. Lined as these parts are by chitin which often bears rough, tooth-like projections and spines, some persons have suggested that in insects where these structures are present in the fore-intestine, the food is masticated more thoroughly and mixed with digestive juices before it reaches the stomach. In the stomach digestion is probably completed and absorp- tion at least begun, but the length of the hind-intestine in many insects THE INSECT: ITS INTERNAL STRUCTURE 17 suggests the idea that absorption in those cases has not been completed when the food leaves the stomach but continues in the hind-intestine. Opening into the mouth is a tube leading to the sahvary glands, which generally lie in the front of the thorax and appear to have a similar func- tion to those in man. In some cases other glands for different purposes are also present in the head or front of the thorax and open into the mouth. Fig. 24. — Internal anatomy of the Honey Bee showing alimentary canal, tracheal and nervous systems, ce, compound eye; hi, hind intestine; hs, honey sac; It, lateral trachea (enlarged); mt, malpighian tubes; nj, rectal glands; s, stomach; sp, spiracles. {Modified from Leuckart's Wandtafeln.) Some of the poisons used in control measures are swallowed by the insect, passing to the stomach and there are dissolved by the digestive juices. Thus dissolved, they set up inflammation of the stomach walls and finally cause death. Poisons acting in this way are called "stomach poisons." Breathing Organs. — Respiration in insects is accomplished by a method which is nearly unique. The oxygen needed, instead of being 18 APPLIED ENTOMOLOGY drawn into lungs and there being taken up by the blood and carried to the parts of the body where it is needed, as in man, is carried directly to those parts by a system of air tubes which open along the sides of the body (Fig. 25). Here the air enters the tubes and proceeds through them to where it is utilized. The openings by which the air enters are called spiracles, and these occur in pairs on some of the thoracic and most of the abdominal segments, varying somewhat in number and in position on the seg- ment in different insects. The spiracles often have valves by which they can be more or less completely closed at will. Each spiracle opens into a short tube or trachea which, with the others of that side, soon joins a similar tube run- ning along the side of the body and quite close to its surface. From these longitudinal tracheae, branches pass off in various directions, and in turn branch again and again until every part of the body is reached by its air supply. The tracheae frequently enlarge here and there, forming so-called air sacs. The tracheae are lined by chitin con- nected with that of the surface of the body. In these tubes, however, it is formed with spiral thickenings which act like a spring, keeping the tracheae open when not under pressure. There is probably considerable pressure on them in different places by the movements of various parts of the body in walking and other activities, as well as by regular respiratory movements, and the resulting temporary variations in diameter aid in the circulation of air in these tubes. Not only are the tracheae of use in carrying oxygen to all parts of the body, but they also receive the carbon dioxid gas produced by the activi- ties of the cells and permit it to escape through the spiracles from the body, thus performing both of the functions which the blood, so far as gases are concerned, accomplishes in man. Blood then, in insects, does not (except in a few cases perhaps) have a respiratory function. The destruction of insects by fumigation is accomplished by the sub- stitution of a gas destructive to life, for the air, and this gas enters the Fig. 25. — Diagram showing ar- rangement of the main tracheal tubes in an insect, a, antenna; h, brain; /, leg; n, nerve cord; p, palpus; s, spiracle; st, branch from main lateral trunk, t, to spiracle; v, ventral branch; vs, visceral branch. {After Kolbe, from Folsom.) THE INSECT: ITS INTERNAL STRUCTURE 19 spiracles and follows along the tracheae to the living tissues, which take it in place of the oxygen usually received in this way, and arc killed. It was formerly supposed that certain materials called contact in- secticides which kill insects by contact with their bodies, caused death by entering the spiracles and closing them up, thus producing suffocation. This has now been proved to be incorrect. Insects which in their early stages live in water, cannot of course breathe air into their bodies through spiracles during that period of their lives. These are closed in such cases and the animal obtains air usually through special structures called tracheal gills. These will be described in connection with the insects which possess them. In a few small water-inhabiting forms, the chitin covering the surface of the body is so thin that oxygen present in the water can pass directly through it into the body and to the parts there which need it, and carbon dioxid passes in the reverse direction. Circulatory Organs. — Insects have only an incomplete system of blood vessels. A tube lies in the middle of the body close beneath the back, beginning near the hinder end of the animal and extending forward into the head (Fig. 26). In the abdomen this tube is constricted, forming chambers, and the chambered portion is called the heart. There is a pair of openings on the sides of each chamber through which blood can enter, and valves there which prevent its going out again. The walls of the heart contain muscles and these contract one after the other, forming a sort of wave of contraction which begins at the hinder end and travels forward. Blood in the heart, being unable because of the valves, to pass out at the sides, is pressed forward by this contraction wave, and at the front end of the heart finds itself in a tube without chambers or valves, called the aorta, through which it is led to the head where the aorta may divide into a few short branches or may be unbranched. In either case, at this point the blood pours out of it into the body, the system of blood vessels coming to an end. There is now no definite and particular path for the blood to follow, but it would, in theory at least, remain near where it escaped from the aorta, or gradually pass into any spaces it might find unoccupied between the different structures in the head. With each heart-beat, however, more blood is poured out of the aorta, increasing the pressure upon that already in the head. It therefore is gradually forced backward and to other parts of the body, each particle probably taking the path where there is least resistance to its passage. In this way a general backward direction is given to the flow. As it approaches the heart, another influence appears. During each contrac- tion of the heart, it occupies less space, which leads to less than normal pressure near it, and blood close by naturally flows closer to it. Upon its expansion again and the opening of its valves, the direction of least resistance is now through the valves and into the heart. As the blood passes back through the body, a given particle may at one circuit go over certain organs and at the next, over entirely different ones. All the internal organs, however, have their surfaces bathed by blood and this as it passes over the stomach or other parts of the alimentary canal will pick up any 20 APPLIED ENTOMOLOGY food which having been digested has passed through the canal walls. Likewise in passing over any organ needing this food, it is given up to those organs. The blood therefore serves as a distributor of food from the place where it is digested to all the parts which need it. We have already seen that the Hving parts of the body — the cells — need oxygen, and as the result of their activities give off carbon dioxid gas, but that this exchange is accomplished by the aid of the tracheae. In a somewhat parallel way, the cells which need food obtain it from the blood. The cells by their Fig. 26. — Diagram showing by the direction of tlie arrows the general course of the blood flow in a Dragon fly nymph, a, aorta; h, heart. {Modified from Kolbe.) activities produce not only carbonic acid gas but also waste material nitrogenous in nature which must be removed like all wastes, from the body. This nitroge- nous waste is picked up at the cells by the blood and carried along , perhaps for some time before a place to dispose of it can be found. Sooner or later, however, a particle of blood containing this waste material will wash over certain structures called Malpighian tubes, to be described in the next section, and the cells which form these tubes have the power to collect this waste material from the blood as it flows over them, thus purifying it. The blood itself is usually a colorless (though sometimes yellowish, reddish or greenish) fluid, in which are corpuscles resembling the white corpuscles of human blood. It appears to serve to carry food to the tissues, and waste matter from them, and therefore has no need of structures in it like the red blood corpuscles of man, the work of which in insects is done by the trachea?. THE INSECT: ITS INTERNAL STRUCTURE 21 Excretory Organs. — The organs which ehminate the nitrogenous wastes from the body and correspond in function to the human kidneys, are known as Malpighian tubes. These are bhnd-ended tubes, the walls of which consist of a single layer of cells surrounding a central channel which at one end opens into the hind-intestine, usually near its front, just behind the stomach (Fig. 27). When blood containing nitrogenous waste matter washes over the outer surface of a Malpighian tube, the cells of which it is composed have the power of taking this matter out of the blood into their own substance and passing it through themselves into the channel between them, down which it moves until it enters the mid-intestine, from which it is finally expelled at the anus. The Malpighian tubes may be few or many; long or short (see Figs. 22, 23, 24). They show a tendency to collect in groups and to unite near the hind-intestine, so that their outlets into this are much fewer than the number of tubes. It seems possible that a certain amount of poison entering the body by way of the stomach can be eliminated by the Malpighian tubes, which may explain the varying degree of resistance to such poisons by different insects. Nervous System. — The nervous system of insects is located along the middle line of the body quite near its under surface (Fig. 22). As in animals generally, it is composed of cells and fibres. The former are for the most part gathered together in clusters which are called ganglia, and from each of the cells in a ganglion, one or more nerve fibres pass out, either to connect with some other nerve cell or with some structure of the body. The larger nerves are really bundles of these fibres running side by side like the wires of a telephone cable. Apparently each segment of the insect body once had a nerve ganglion, tnit with the fusion of the segments, many of these have also fused, reducing the separate ganglia in adult insects to a smaller number, which varies in different kinds. This fusion has been produced by the hinder ganglia moving forward until in some cases none are found in the abdomen. Different degrees of this are shown in Fig. 28. Each ganglion is connected to the one in front and the one behind by one or two bundles of nerve fibres which are called commissures. Each consists of numerous fibres and these taken together form the means of communication between the different parts of the system. In the head, in front of or above the oesophagus, is the largest gangUon of the body, called the brain, produced by the fusion of several ganglia. In addition to its two commissures, which connect it with the ganglion next behind, it has nerves which lead to the eyes, to the antenna) and to other parts of the front of the head. Fig. 27. — Portion of the Malpighian tube of a fly, greatly enlarged, k, cell nucleus; /, lumen of the central canal; tr, trachejE. (Modified from Gcgcnbaur.) 22 APPLIED ENTOMOLOGY Below or behind the oesophagus is a second ganghon, also in the head, called from its position the suboesophageal ganglion. As the oesophagus lies directly between this and the brain, the commissures connecting the two do not lie close together, but separate far enough to permit the oesophagus to pass between them. The suboesophageal ganglion besides being connected with the brain in front, and the first thoracic ganglion behind it, by commissures, sends nerves to the mouth parts and other nearby regions of the head. Fig. 28. — Diagram showing various degrees of concentration forward of four species of flies. A, of Chironomus plumosus, little concentrated; B, Empis siercorea; C, Tabanus bovinus; D, Sarcophaga carnaria, most concentrated. {After Brandt, from Lang's Lehrbuch.) The thoracic ganglia may be more or less separate or fused and may have fewer or more of the abdominal ganglia added. Commissures, however, connect all separate ganglia, and these also send out nerves to all the parts of the segments to which they belong, no matter what their final location may be. In this way, the wings, legs, muscles and other parts receive their nerve supply. A small "sympa- thetic nervous system" also present, appears to be concerned chiefly with the nerve supply of the alimentary canal and trachese. Sense Organs. — All the more evident senses possessed by man appear to be present in insects, but not in all cases in the same individual. Thus some cave- inhabiting insects have no eyes. It is at least probable that insects may have other senses not possessed by man. Reproductive Organs. — Insects are of distinct sexes, male and female. In many cases, however, individuals occur, incapable of reproduction, their sexual organs not having become fully developed, and such insects may be termed neuters. Most of these appear to be really undeveloped females, though undeveloped males are also known. They are found in colonial insects where division of labor occurs, as in the honey bee, ants, termites, etc., and are known according to their duties, as workers, soldiers, i THE INSECT: ITS INTERNAL STRUCTURE 23 or by other names. Conventional signs for the various forms of insects as a convenience, are : cfmale; 9 female; 9 worker. In the female (Fig 29) the eggs are produced n a pair of ovaries located in the upper front part of the abdomen. Each is a cluster of ovarian tubes whose walls are cells. Some of these cells grow and separate from the others to lie in the central cavity of the tube and then pass downward, growing till they reach its hinder end, which connects with the similar ends of all the ovarian tubes of that side to form a single tube called the oviduct. This extends downward and back- FiG. 29. Fig. 30. Fig. 29. — Female reproductive organs of Honey Bee {Apis rnellifera L.) ; ay, accessoiy gland; o, ovaries; od, oviduct; j)g, poison gland; r, rectum, cut off and end bent back; sr, seminal receptacle; v, vagina. {Modified from Leuckari's Wandtafeln.) Fig. 30. — Male reproductive organs of Honey Bee {Apis Mellifera L.) ; off, accessory gland; ed, ejaculatory duct; s, spermaries; vd, vasa deferentia. {Modified from Leuckart's Wandtafeln.) ward around the side of the alimentary canal, below which it joins with a similar oviduct from the other side of the body to form a single duct, the vagina, which lies below the ahmentary canal, and extends backward to its outer opening which is located in most cases, in front of the next to the last abdominal segment. Surrounding this opening may be external structures (an ovipositor) for the pur- pose of together making holes in some object (the ground, wood, etc.) in which to deposit the eggs. A side pouch (seminal receptacle) connected with the vagina is for the storage of the sperms wh ch fertilize the eggs; a gland producing material which forms the egg shell and is known as the shell gland, alsp opens into this portion, and other glands similarly connected with the vagina, may also be present. 24 APPLIED ENTOMOLOGY In the male (Fig. 30) the arrangement of the organs closely corresponds to that in the female. A pair of spermaries or testes is present in the upper front part of the abdomen, each consisting of a rather closely-coiled mass of tubes, in which the sperms are produced. The tubes on each side unite to form a single tube, the vas deferens. These differ from the oviduct usually, in being much longer and coiled or twisted. They pass downward and backward, however, and unite on the middle Hne of the body below the alimentary canal, forming a single tube, the ejaculatory duct, corresponding to the vagina in position, which leads back- ward to an opening in front of the last segment. An enlarged portion of the vas deferens is often present, for the temporary storage of the sperms, and is termed the seminal vesicle. Accessory pouches opening into the ejaculatory duct appear to be in part at least, for the production of mucus and secretions to mix with the seminal fluid. ."■*?# CHAPTER IV THE DEVELOPMENT OF INSECTS Most insects lay eggs which hatch after a longer or shorter time into the young. In some cases the egg appears to be retained within the body of the parent until after it has hatched, and then the young are produced in a stage able to move about. Insects in which this is true are termed viviparous, the others being oviparous. Insect eggs are usually very small ; vary greatly in form, and may be laid singly or in clusters (Fig. 31). They are covered by a chitinous shell, the chorion, which often bears markings in the form of ridges, Fig. 31. — Eggs of various insects. A, butterfly; B, house fly; C, chalcid {Brucho- phagus); D, butterfly; E, midge; F, bug (Triphleps) ; G, bug (Podisus); H, Pomace fly. All much enlarged. (From Folsom.) reticulations, etc., and frequently they are also colored. At one place on the surface is a minute opening or group of openings through the shell, called the micropyle, believed to be for the entrance of the fertilizing sperm. The length of time spent in the egg differs in different insects from a few hours to many months, and in some cases the eggs do not hatch until the second season after they are laid. In hatching, the shell breaks and out of it crawls the young insect, in the majority of cases quite unlike the adult it is to become. In order to reach maturity it must now grow, and undergo changes in structure and appearance. These together are expressed by saying that most insects in order to become adult undergo a metamorphosis. In some of the simpler insects, a few changes and growth only, are needed to make them mature, and these are therefore usually grouped together as the Ameta- bola, or insects having practically no metamorphosis. 25 26 APPLIED ENTOMOLOGY The remaining insects, from this standpoint, form two groups: those which on hatching show some resembhmce to the adults and reach matu- rity by a certain series of changes; and those which on hatching are totally unlike the adults and attain that condition in a different way. These groups are known as the Hemimetabola or Heterometabola, and the Holometabola respectively, these names suggesting the amount of metamorphosis required for members of each group to become adult. A member of the group Ametabola, upon hatching, will begin to feed and grow. Growth, however, is restricted because the insect is enclosed by chitin which, while elastic to some extent, at least at its thinner portions, has its limitations in this regard. In some cases the insect is able to reach its adult size within the chitin, but in other cases this proves impossible, and a process called molting takes place. This is begun by pouring out of fluid by the outside layer of living cells, the hypodermis, between it and the chitin, separating the two. Next a split in the chitin appears somewhere, usually along the back, and the insect crawls out of its skin, i.e., molts. It is now soft and unrestricted by an outer shell and grows rapidly. A new chitinous shell begins to appear and is completed in a short time (within a day or so) and thereafter only such growth is possible as the elasticity of the new shell will permit. In most of the Ametabola, molting as thus described is not usual, the shell being sufficiently thin to stretch the amount needed for growth to adult size, though sometimes two or even three molts may occur. In both cases, however, the reproductive organs appear not to be mature at the time of hatching, and only gradually beconie so during the period following. In a few cases molting seems to occur at intervals throughout hfe. In the Hemimetabola (or Heterometabola) the young insect on es- caping from the egg, though resembling its parent to some extent, must nevertheless undergo many changes in structure and a considerable increase in size as well, before reaching maturity. Thus a young short- horned grasshopper, on hatching, will need to grow to be about ten times as long before becoming adult; it is without wings, which will need to be developed; its reproductive organs are not mature and must become so, and other differences occur. All of these must be transformed into their condition in the adult, and to accomplish this, energy is necessary. In the egg the energy for development had been provided by the yolk: after hatching the young insect must provide it by gathering food. The young insect therefore, soon after hatching seeks for food, and having found it begins feeding. The nourishment thus obtained results in growth so far as this is possible within a shell which is tightly fitting and only to some degree elastic. When no further growth in this way can occur and the body has stored within it all the materials needed for a greater increase in size, it proceeds to molt in the manner already de- THE DEVELOPMENT OF INSECTS 27 scribed for the Ametabola. On escaping from its old skin or shell, how- ever, besides a rapid increase in size, changes of structure also occur, so that a difference in appearance now becomes evident. These changes must be produced quickly, as the hypodermal cells of these parts, as well as of all the surface, are producing a new chitinous skin, and when this has once hardened, no further changes and little further growth are possible. Molting then, marks the beginning of a brief period — a day, more or less — of increase in size and of changes in appearance, these last all being in the direction of making the young insect more nearly like the adult it is to become. When the new shell has become hardened the insect resumes its feeding. After another feeding period the young insect is again confronted with the same difficulties as before, and it meets them in the same way, by molting, and immediately thereafter, before its new shell has hardened it seizes the opportunity to grow and change its appearance further. Finally, after some molt, full adult size for the insect is attained and all its organs have also fully developed and matured, producing the adult insect itself. Thus the young insect becomes an adult by alternating periods of feeding, with brief periods of molting, following which growth and change take place, the total of which produces the adult. The number of molts and consequent opportunities for change which occur, varies in different Hemimetabola. There may be only two or three in some kinds: five is perhaps the average number though more are not uncommon, and 21 are known to occur in one species. Certain names for these different conditions are convenient for use. The feeding periods between the molts (or ecdyses) are called instars, so that the progress of an insect from hatching to adult is by an alternation of instars and molts. The insect itself, from hatching until maturity is generally called a nymph. Figure 32 shows the changes in size and appearance of a grasshopper after each molt. With the remaining group of insects, the Holometabola, while there is a little similarity in the metamorphosis to that in the Hemimetabola, there are also many differences. When a young Holometabolous insect hatches, it in no way resembles its adult. A caterpillar is totally different in appearance from the butter- fly it finally becomes : the white grub in the earth is in no way suggestive of the June bug (May beetle) into which it transforms. Nevertheless it has to meet the same problems of growth and transformation to the adult condition as do the Hemimetabola, and uses the same means for accomplishing the needed results, viz., the utilization of the energy derived from its food. Accordingly, upon hatching, in the Holometabola, a feeding period or instar comes first, followed by a molt and growth. At this point the 28 APPLIED ENTOMOLOGY story of the metamorphosis differs from that of the Hemimetabola, for after the molt no change in appearance to make the young insect more nearly like the adult takes place. It may be different in some regards besides size, from what it was before the molt, but these differences do not increase its resemblance to what it finally becomes. This holds through- out the feeding period of its existence, so that after three, four or more molts, a caterpillar is still a caterpilar, a grub is still a grub, and this is equally true for all Holometabolous insects. Within the insect during this period, however, changes not perceptible on the surface are taking place, by the construction of portions of the adult which are forming as Fig. 32. — Incomplete metamorphosis of a Grasshopper, a, first nymphal instar; b, second instar; c, third instar showing beginning of wings; d, fourth instar; e, fifth instar; /, adult. Figures not drawn to same scale. (Modified from Packard's Text-book of Entomology by perm.ission of the MacMiUan Com,pany, Publishers.) buds or ingrowths from various parts of the body, and are termed imagi- nal buds (from "imago," the adult). They are closely compacted and many at least are infolded somewhat like buds, becoming finally ready to open when the proper time comes. And during its feeding instars, the larva, as the young insect in the Holometabola is called, is not only storing energy from its food for its growth at each molt, but also to carry it on through a period yet to be described, during which it must transform into the adult condition while unable to feed and obtain the energy needed for this purpose. After a varying number of feeding instars and molts, the young insect or larva has grown sufficiently and has stored within it energy enough to carry it through the remainder of its changes, and internally the essential parts for the adult condition have been formed as far as THE DEVELOPMENT OF INSECTS 29 possible under existing conditions. As the next change will produce an animal practically helpless in most cases, and unable to protect itself from its enemies, its next step is to find as much protection as possible. Accordingly, the full-grown larva usually, though not always, leaves the place where it has been feeding and elsewhere prepares for its next change. Many larvse begin this by spinning around themselves a thread of silk, produced by glands within the body and opening to the surface on the lower lip. This thread is spun backward and forward and around the body until it sometimes forms a complete outer covering, entirely concealing the larva within, from view. This case or cocoon appears to be protective in its function. Some larvae go under ground for this change. Here a cocoon, as such, seems unnecessary, but after digging into the earth a few inches, the insect forms a little earthen chamber or cell in which to lie, and generally lines this more or less densely with silk, probably to keep the earthen walls from falling in and crushing it. A larva transforming in tunnels in wood where it has fed, may make a partial cocoon with more or less of the chewed-wood fragments mixed in. One staying above ground but not in tunnnels or otherwise protected, will spin more or less of a cocoon as already described. The completeness of the cocoon, however, varies greatly with differ- ent insects. Instead of being a thick, dense wrapping which entirely conceals the insect, it may be so scanty that the animal within can be seen to some extent. In other cases it is merely a sort of network, in no degree giving concealment; and in still others, a few scattered threads to hold the insect in place are all that represent it. Sometimes hairs from the body of the larva, held together by silk, form most of the cocoon, and in the case of butterflies, only threads enough to attach the hinder end of the body at the place where it is to transform, and to form a supporting loop around its middle, the ends of the loop also being fastened to what it rests on, are produced. In some flies the larva shrinks within its larval skin and transforms, this skin, now called a puparium, fimction- ing like a cocoon (see Fig. 33c). The reason for such variations in a structure presumably formed for the purpose of protection, can only be guessed at. Possibly in the course of generations, some insects found less need of this than others and gradu- ally reduced it, thereby saving the vital energy so much needed for trans- formation, which would otherwise be expended in cocoon making. Whether the larva forms a dense or scanty cocoon, or none whatever, the next step in the process is a molt. When the insect escapes from this skin, however, a great change in its appearance is evident, and it is now called a pupa (Fig. 33a and b). In a general way it may be said that it has at this one molt changed more than half way to its adult condition. This is due in part at least to the unfolding of the imaginal buds already 30 APPLIED ENTOMOLOGY referred to, which contribute largely to form the new surface of the body in which head, thorax and abdomen are evident, as are also the antennae, legs, stubs of wings and other adult structures. Many of the internal organs of the larva though, were necessary for use till the last moment before it became a pupa. Then too, tha arrangement of the muscles, in the larva, would not be that needed by the adult. Accordingly, most of the internal organs now gradually break down, losing all their earlier form and structure, and new ones to meet the needs of the adult are con- structed to take their place. Fig. 33. — Different types of pupation, a, pupa obteeta of a moth; b, pupa libera of a beetle; c, puparium of a fly. a and b about natural size; c much enlarged. (Original.) During this breaking down and the reconstruction period, the pupa is practically helpless in most cases, hence generally the need for the protecting cocoon or earthen cell it constructs. When the structure of the adult insect has been completed, another molt takes place, the pupa skin splitting and setting free the insect. If it was enclosed in a cocoon it now produces a fluid which sufficiently softens the silken threads so that it can push its way out and it escapes or "emerges." It is now soft, its wings are only partly expanded, as in most cases there would be no room for full-sized wings in a pupa, and because of its reconstruction there is considerable waste matter in its body. The insect crawls upon whatever it may find to hold on to, expels the waste matter, and its wings begin to grow rapidly. Drying out also takes place and in a short time (a few hours) the adult thus produced is in every way fully matured. To summarize the differences in metamorphosis of the three groups it may be said that in the Ametabola the insect hatches from the egg prac- tically in an adult condition, i.e., there is little or no metamorphosis. In the Hemimetabola the insect hatches from the egg in a form somewhat resembling the adult but much smaller. It becomes adult by alternating THE DEVELOPMENT OF INSECTS 31 periods of feeding with molts, at which times growth and changes bringing it nearer to the adult occur, the last molt completing the growth and adult structure. In this life history we have a change, but as there was a resemblance to the adult from the start, the change to it (metamorphosis) is only an incomplete or partial one. In the Holometabola the insect hatches from the egg in a form totally unhke the adult, and while feeding periods followed by molts and growth give increase in size, no external evidence of any changes making the insect more like the adult can be found. These changes are largely made after the end of the feeding and growing periods during a pupa (generally quiet) stage, in which the breaking down of the larval, and construction of the adult structures is completed. The difference between the larva on hatching and the adult is so great that an entire change (complete metamorphosis) takes place. It should be evident from the foregoing that when the adult condition is once reached, little if any growth is possible (except in rare cases) and that the belief so common, that "big flies grow from little flies," is without any basis of fact. The nymphs of the Hemimetabola appear not to have attracted sufficient attention to have received any special common names. In the Holometabola the larvae of various groups differ greatly in appear- ance; many are large and noticeable and some of them have, as a result, received special names. Larvae of butterflies and moths are commonly called caterpillars; those of beetles are usually called grubs; those of flies are called maggots. Larvae found boring in wood, however, whether they will become moths, beetles or other insects, are uniformly called borers. In the Hemimetabola then, the stages of life are: egg, nymph, adult; in the Holometabola they are: egg, larva, pupa, adult. Whether or not the pupa is enclosed by a cocoon depends upon circumstances. CHAPTER V LOSSES CAUSED BY INSECTS : NATURE'S CONTROL METHODS To asctu'tain how much man loses by the attacks of injurious insects is a difficult task. The destruction, either partial or entire, of his crops both growing and in storage; of household goods and of food; of our forests and of the wood cut therefrom; injuries to our domestic animals and their products: these and other injuries can be more or less accurately estimated. But when we consider the attacks upon man by disease- carrying insects, resulting in loss of time from productive labor, or even by death, and the actual costs connected with illness, the problem becomes extremely complicated, and to determine how much financial loss this country suffers from insects is a matter for the economist as much as the entomologist. Much of this loss ws fail to appreciate, never having had a season free from the attacks of insects which might serve as a standard for comparison. If we could once have such a year entirely insect free, however, the difference would at once force itself upon our notice. Crop Losses. — Careful studies of the crops injured by insects have now extended over quite a term of years, and the general conclusion rsached is that in an average year with no unusual attack, a crop will generally produce only about nine-tenths as much as would probably have been the case had insects not been present. When an outbreak occurs, this will decrease production below that point, and instances are far too frequ.mt where for a single crop of some kind, production has been only 20 or 30 per cent of the normal, and many cases are on record where in some localities the destruction has baen complete. This estimate covers field crops; destruction of forests and forest products; attacks on domestic animals and their products; articles in storage; on shade trees, shrubs and ornamental plants; on farm wood lots which are not included with the forests; on household goods and foods. With fruit and truck crops the destruction and injury is believed to be more than one-tenth generally. Health Losses. — A number of serious diseases of man are due to insects which serve as carriers of the disease-producing organisms. Among these are malaria, the typhoid, typhus and yellow fevers, and the bubonic plague, besides others of less importance. Illness with any of these diseases means that the patient is not only unable to work but is an actual cause of outlay for nursing, treatment, and possibly death expenses also. With hundreds of thousands of illnesses from these 32 LOSSES CAUSED BY INSECTS. NATURE'S CONTROL METHODS 33 diseases each year, the loss of time from productive labor is, of course, very large, and the country is that much poorer than it should be. Death puts an end to any further production by those concerned, and here also is a loss to the country. It has been estimated that the loss of labor by sickness and death, caused by malaria alone, is at hast $100,- 000,000, and by all insect-borne diseases is over $350,000,000 each year in the United States. In addition, there are many places in this country where th(^ soil is rich and would pay well if cultivated, but where man cannot live under existing conditions because of the presence there of insects and the diseases they carry. DifEiculties in Estimating Losses. — To fix a monetary value for all this destruction and injury, however, is a difficult problem, so many fac- tors enter into it. It cannot be denied that insect attacks result in a direct reduction of wealth to the country as a whole; that whatever food material has been consumed by insects is not available for consumption by the people, is self-evident; and that if on account of a resulting scarcity of any food the consumer pays more for it, he is thereby paying toward the cost of the ravages by the insects. The producer of this food though, may because of the reduced amount available, be getting as much or even more than he would have received had insects not destroyed any of it. In other words, while the destruction of any crop caused by insects is cer- tainly a loss to the nation as a whole, those fortunate individuals who suc- ceed in raising that crop may receive as much or more for the amount they did produce than would otherwise have been the case. On the other hand the man who starts to raise such a crop and loses a large percentage of it by insect ravages, may not have a sufficient amount left to repay him even at the higher prices, for his expenses. It is evident then, that insect ravages while meaning a loss to the country as a whole, may also mean either a loss to producers, a normal profit because of a higher price on what part of the crop they have been able to save, or even a better profit, due to higher prices than could other- wise have been obtained. No crop producer can as yet foretell whether he in any given year will be one who will lose, receive a normal return, or do better than usual on any of his crops. He can only be prepared for insect attacks if they come, and save all he can by proper methods of protection and repression, know- ing that the vast majority of the people will do little or nothing in this line and that in consequence he will be among those losing least; will have proportionally more to sell, and that he will therefore receive the benefit of any higher prices coming from a reduced production. Against what he will gain in this way must be offset the cost of his protective and control measures. If these are too expensive he will gain nothing, but in most cases their cost is small as compared with the value 3 34 APPLIED ENTOMOLOGY of the product saved, and such measures used with judgment represent one of the cheapest and most successful forms of crop insurance. It is certain that the time will never come when protection of crops from insect ravages will ever be so universal and successful that to produce crops will not pay, for with our increasing industrial population to be fed the demand is more likely increasingly to exceed the supply, even though every crop producer should finally come to the protection of what he raises, from insects. At present the farmer who adopts modern methods against insect injuries is certain in any term of years to raise more and to sell at higher prices than one who trusts to chance or "luck" in this phase of his induvstry. Figures on Losses. — From the above it becomes evident that no accurate figures as to the losses caused by insects can be given. We can only recognize that everj^thing produced which is destroyed by these pests is thereby lost to the country as a whole, even though some individuals may profit. To value this destruction we have only the prices for which crops sell, as a criterion, and the point has already been brought out that if the tenth destroyed had been saved, the price of the whole might have been no greater than it was for the nine-tenths actually produced. Tak- ing this unreliable standard, however, in order to get some slight idea of the amount of destruction ordinarily caused by insects, we may bring together the following statement, based on the average value of the crops for the five years 1913-1917 as given in reports of the United States Department of Agriculture and from other sources. Field crops $833,660,000 Animals and their products 431 ,450,000 Forests, forest products and materials in storage 300 , 000 , 000 Loss by human disease and death 350 , 000 , 000 Farm wood lots 100,000,000 Extra losses on fruit and truck crops ? Shade trees and ornamental shrubs and plants ? Household goods and foods ? Altogether, if we may accept figures based on the assumption, as has been indicated, that if no losses had occurred the value of the whole would be at the same rate as the actual price for what was obtained, it is safe to estimate the loss in the United States due to injurious insects as being not far from two billion dollars each year. How nearly correct this is, however, no one can tell, so many factors enter into the problem. Causes of Increased Injury. — Losses to crops, forests and other mate- rials are increasing, for several reasons. Before the settlement of this country there were, of course, native insects attacking the various plants growing here. When settlements were established new plants were intro- duced by the settlers and grown in greater abundance than if they were LOSSES CAUSED BY INSECTS: NATURE'S CONTROL METHODS 35 wild and scattered. An insect finding in any of these a food acceptable to it, would at once also find a more abundant supply, and a rapid multi- plication would become possible, resulting in their increase to injurious abundance. A second factor has been the introduction of many insects from foreign countries. In the United States such forms have sometimes entirely failed to maintain themselves. Unfortunately, as has more fre- quently happened, they have found all conditions favorable to a rapid increase, unchecked by their enemies which in most cases have not also been l)rought to this country with them. A third factor has been that with the increasing occupation of this country, much of its wild bird life has either been destroyed or has been driven away from tlu^ neigh])orhood of man. Many insect feeders among birds, once quite common, must now be sought in remote woodlands and thickets, and rarely show themselves near settlements. Some kinds have adjusted themselves to the new conditions and among these may be mentioned the robin, chipping sparrow, blue bird and a few others. But to too great a degree the insec- tivorous birds are l^ecoming either fewer in number or afraid to visit the settled districts where cats and people are numerous, even though in such places the gardens and trees may be thickly populated with insects. With modern agricultural methods distinctly favoring a rapid in- crease of insects by providing an enormous acreage of a single crop;' with an addition to our worst native pests of at least as many more from other countries, which have escaped their enemies by coming here; and with our birds becoming less effective in their work, it is only natural that losses by the attacks of insects should be great and increasing in importance. Control by Natural Methods. — In countries undisturbed by man and his industries it is prol)able that destruction or serious injury from insect attacks would usually be rather small, particularly in a series of years. The saying in Physics that "Nature abhors a vacuum" seems to be paralleled in Biology by the paraphrase, "Nature abhors extermination." Accordingly, insects appear to be more or less com- pletely held in balance by natural factors, some of which may be briefly considered here. Plants of various kinds form the food of most of the insects which we regard as pests, and in a country entirely under natural conditions, plants of any one kind are liable to be more or less scattered, no large number being close together. Under such conditions a search for the proper food plant is necessary to an insect as a preliminary to egg- laying, and in many instances these may be too scarce to provide for all the insects. In any case, where the food supply is scanty, an insect 1 As an example of this, apple orchards containing thousands of trees are now common. It is stated that one year in a single valley in California, there were three wheat fields each containing over twenty thousand acres. 36 APPLIED ENTOMOLOGY species feeding wholly on that kind of plant will be more rare than where its food is abundant. If, on the other hand, there is an abundance of the food plant, there is a greater probability of the survival of more of the insects. But this brings its disadvantages. Increase in the number of the insects will result in more food being needed, and finally this will become insufficient and will be followed by the failure of many to find food, death resulting. In this way a balance may be finally secured, though it will not be permanent, the process being repeated in the subsequent years. Weather conditions are also a factor in Nature's control. Some insects find in a wet season conditions favoring the survival of a large proportion of those which appear, while for others such a season produces heavy mortality. A severe winter with many and marked fluctuations of temperature may put an end to the rapid increase of some species which because of preceding favorable winters, has been becoming more abundant. Other meteorological factors also enter into the subject of insect control. Birds and other animals which feed on our insects must also be con- sidered in this connection. When insects acceptable to these animals are abundant, more will be eaten and in any case many will be destroyed in this way. Where insectivorous birds have an abundant food supply more will survive, which will result in more individuals to be fed. Thus an abundance of insects may lead to a corresponding increase in abun- dance of their enemies. Parasites and diseases play their part too in this competition. The more abundant an insect becomes, the more food is thereby available for its parasites, and fewer of these will fail to find an insect to attack. Finally the parasites may become so numerous that practically all the insects of the kinds they attack will be found and killed. The next generation of parasites following this, will, of course, consist of many more individuals than the one preceding, but now so many of their food insects or "hosts" have been killed in producing them that there are practically none left, and most of these parasites die for lack of food. Thus, under these conditions, a sort of "balance of Nature" develops, and though the scales may tip first to one side and then to the other, this balance is usually preserved if periods of a number of years at least, are considered. But when man with his many lines of activity appears in the field, introducing and raising millions of plants of the same kind in small areas, instead of scattering them here and there, thus furnishing enormous quantities of food for insects; and when he brings in many pests from foreign countries, no matter how unintentionally, which in their new home are not beset by the foes present in their native land; and when LOSSES CAUSED BY INSECTS: NATURE'S CONTROL METHODS 37 his manner of life is such as to drive away birds which might be valuable aids in his struggle against pests, the situation changes rapidly for the worse. Those who look on the bright side are confident that in time Nature will reestablish a balance, and this is probably true. But Nature works in centuries, and man cannot wait so long for results. Under these conditions artificial measures as contrasted with natural ones must be taken if crops are to be raised, food obtained, and if health is to be preserved, and these artificial methods for the control of injurious insects need to be known, and the nature of their action understood. CHAPTER VI ARTIFICIAL METHODS OF CONTROL It has been indicated that Nature has methods for the control of any- continued undue abundance of insects, by a resulting scarcity of food; by weather conditions; by insectivorous birds, and other animals; by parasites and diseases; and probably in other ways also. But it seldom pays to wait for the results so obtained, as they generally require a num- ber of years for completion, and measures which may be termed artificial, inasmuch as they are used by man, also have their value. These measures may be divided into two groups, viz., those which aim to establish conditions unusually favorable to the plants or un- favorable to the insects; and those which attempt either to poison or otherwise directly kill the insects. In some cases perhaps, a given treat- ment might seem to belong as properly in ona of these groups as in the other, but in general the line of separation is quite distinct. Whatever the method and its effectiveness may be, there is always the cost of using it to bear in mind. When this cost is greater than the loss would otherwise probably amount to, it is evident that little will be gained by treatment, except that in such cases possibly, omitting it for this reason one year may result in such an increase of the pest as to pro- duce serious results the following season. In other words, treatment costing more than the probable loss may sometimes pay as a sort of in- surance. In general, though, in every case where insect attack occurs, the estimated cost of the treatment should be weighed against the probable loss without it, in deciding whether to treat or not. GENERAL FARM PRACTICES These are chiefly methods for raising crops which distinctly increase their vigor and growth or remove conditions favorable to insects. Healthy crops, clean culture, the rotation of crops, late or early plowing, and the time of planting are the chief farm practices which belong here. Special methods for particular cases, directed more with reference to the insects than to the handling of the plants, such as hand picking, the use of repellents, burning insects, heat, trap lanterns, etc., may also be in- cluded here, leaving the measures dealing with insects by the use of poisons and by fumigation for later consideration. 38 ARTIFICIAL METHODS OF CONTROL 39 Healthy Crops. — In the majority of cases a vigorous, thoroughly healthy plant is not only better able to withstand insect injury but is also less liable to attack than one enfeebled or not thriving for any reason. Thorough cultivation, the use of fertilizers and the removal or repair of injured or diseased parts or plants as soon as th^se appear, will aid greatly in insuring the desired results. Clean culture is also an important factor. Weeds not only interfere with successful crop growth but may in some cases at least, consiime plant food in the soil which might otherwise be utilized by the crop, thus reducing its vigor, and in addition they provide wintering places for many insects. Rubbish left on a field after the harvest often serves the same purpose: insects frequently find protection during the winter in tall grass too often left surrounding the trunks of fruit trees, and many serious pests winter close to the ground in grass fields. Decaying fruits and vegetables harbor insects and should be composted. Weeds should therefore be killed and burned and the grass kept down in or- chards. Burning over grass fields in early spring in the Northern states at least, choosing a time when the dead growth is dry enough to burn while the living parts of the grass are still so wet as to be uninjured by the heat is often a valuable way in which to destroy many pests which winter there. Clean culture in all its forms, not forgetting fence-line and road- side growth will do much to reduce loss by insects. Crop Rotation. — The rotation of crops often has an important bearing on insect control. Any crop attacked by a particular species of insect should not be followed by another, either of the same kind or by a differ- ent one which is also fed upon by that species of insect. How far this principle can be carried out in practice, however, is a different matter. To break up sod land and plant corn for the first crop is merely to follow a mixture of grasses with a single kind of a grass and from the standpoint of insect control at least, is unwise. It is the usual practice though, and how far it would be wise to depart from it, planting beans, buckwheat or I>erhaps potatoes instead, is a question, though these last-named crops would be much more likely to be free from insects. The entire subject of crop rotations which are satisfactory from the standpoint of agri- culture and are also correct when insect problems are considered, is still in a far from settled condition, and needs prolonged investigation. Plowing.^Many serious pests winter in the ground. Fall plowing after they have formed the cells in which they pupate or winter, as the case may be, will break many of these and remove the protection they give : eggs laid in the ground will often be buried so deeply that the larvae if they hatch in spring will be unable to reach the surface. Similarly, thorough cultivation in the summer, where it is possible, besides being good for the crop, has an injurious effect on insects there. In some cases early fall plowing gives the best results : in others, late 40 APPLIED ENTOMOLOGY fall is the best time. Sometimes disking with a harrow can be done where plowing cannot, and is of value. Time of Planting. — This is sometimes of importance as a protection against pests. Thus, in general, wheat sown after September 20 will escape the attacks of the Hessian fly : early planting will often give cotton an opportunity to obtain the greater part of its growth before the boll weevil has progressed far in its ravages, particularly if early maturing varieties of cotton are planted. It follows from this that a choice of the variety to plant is also often of importance, and insect-resistant varieties of our various crop plants and trees should be selected as far as any are known, if they are otherwise satisfactory. The " bugless potato," while perhaps non-existent, expresses an idea which should be kept in mind, and resistant varieties of plants should be watched for and preserved. Trap Crops. — In some cases trap crops can be made use of to advantage. A small patch of kale planted in the fall, or of mustard planted early in spring will attract the Harlequin cabbage-bugs as they leave their winter quarters, and on these they can be destroyed, as they seem to prefer such plants to the young cabbages. Several similar cases are also known where trap crops work well. Hand Picking. — In some cases, where the pest is large, easily seen, or not present in large numbers, hand picking is the easiest method of control. Egg clusters are often of such a color, size, or have such notice- able features that they are not difficult to find, and the convenience of destroying several hundred eggs at a time, as compared with killing the same numbsr of insects after the eggs have hatched and the young have scattered, is evident. Larvae feeding in groups together are also often most easily destroyed by hand picking. Repellents. — Inert materials, such as air-slaked lime, flour, or even fine road dust, thickly spread over plants will, in certain cases, act as repellents, driving insects elsewhere to a greater or lesser degree. Car- bolic acid, naphthaline, oil of citronella, and other materials having an objectionable odor act as repellents to some insects. Trap Lanterns. — These have been quite extensively tested, but have failed to be as successful as was expected. Though many insects are attracted to such lights, the greater number are found to be beneficial, while of the injurious kinds a large number have already laid their eggs and are therefore no longer of any importance, and most of the serious pests are not attracted at all. On the whole it is doubtful if the use of trap lanterns ever pays. Burning Insects. — Gasoline torches for burning egg clusters, cater- pillars, scale insects, etc., on trees, have also been tried, but the time necessary to kill the insects in this way is often long enough to injure the tree where the blast hits it, and this method must be regarded as at ARTIFICIAL METHODS OF CONTROL 41 least exposing the plant treated, to the risk of greater injury than that caused by the insects. Heat. — Heat can sometimes be used to advantage for the destruction of insects. A temperature of 125°r. is enough, if maintained for 3 or 4 hr., to kill insects infesting grain, seeds, etc., and also almost all house- hold pests at least. Where heat can be applied in this way, therefore, it is a special method of control of considerable value. Miscellaneous Methods. — Borers in trees present particular difficul- ties, being so hard to reach, and cutting them out by hand is frsquently the best control method. Protective coverings over or around plants may sometimes be used to advantage, as for example, netting over young cucumber and squash plants. Sticky bands placed around the trunks of trees keep insects which cannot fly from crawling up to the leaves. Pieces of bark or boards on the ground near plants, under which insects may crawl for protection at night, as some do, are good traps for such insects, if these traps are visited early in the morning and the insects destroyed before they scatter again for the day. Burlap bands around tree trunks attract many caterpillars as being good hiding places during the day. These and munerous other special methods for the control of insects are made us3 of, many being based on some peculiarity of habits of the special pest for which they are used. Still other methods will be considered later, in connection with the insects against which they are used. In order to make proper use of the above methods of Farm Practice, a clear understanding of the life and habits of the insect to be controlled, must be had. Failure in this might easily lead to doing just the wrong thing. The control of insects is at the present time very unequally developed for different crops. Naturally the insects of those which are most valuable have been most carefully studied, those of less importance having been given much less attention. Fruit and market-garden crops have a high value and the insects which attack them have beeii carefully investigated, though the area they cover is very small as compared with the wheat acreage of this country, for example. Trees, bushes or other plants, whether growing alone or in rows with cultivated land or grass surrounding them are accessible as units on which to work, but a 10-acre field of clover, wheat or any other crop, is a totally different proposition. The former can be reached in all its parts by a spray or other treatment : a wheat plant in the middle of a field may need treatment but to reach it would probably cause a greater amount of injury than would be saved by the treatment. Field crops and particularly grain crops therefore, present distinct 42 APPLIED ENTOMOLOGY problems, and here Economic Entomology and Practical Agriculture have failed to work as closely together as should be the case, and our present methods for controlling field crop insects are less effective than with most others. The same thing is true with our forests. The shade tree can be sprayed if that is a desirable treatment, but the spraying of forests even if practicable from the standpoint of expense, is frequently impossible because of the nature of the ground on which the forest stands, density of growth and other factors, and other and more indirect methods of insect repression then must be resorted to. CHAPTER VII INSECTICIDES IN GENERAL: STOMACH POISONS Though the farm practices and special methods outhned in the pre- ceding chapter are of great importance for the control of insect pests in many cases, they are ineffective and cannot be made use of in many others. Under these circumstances other methods of attack must be resorted to, and in general, insecticides of various kinds, fitting the particular nature of the injury and of the insect causing it in each case, have proved successful. Insecticides are substances which may be placed upon a plant, or elsewhere, to be eaten by the insect and which when eaten, kill the insect; or materials which on coming in contact with the body of the insect, kill it as a result of that contact. Poisonous gases and vapors v/ould also be included as insecticides, as thus defined. CLASSES OF INSECTICIDES The materials used as insecticides fall into two general groups: (1) Those which are placed upon the food eaten by the insect, swallowed Avith it, and which upon entering the stomach are dissolved, producing inflammation and finally death. Such poisons can, of course, be used only for insects with chewing mouth parts which bite off and swallow solid food, such as pieces of leaves, stems, etc.; (2) Those which, when they come in contact with the body of an insect either enter the spir- acles and penetrate their chitinous lining and kill the tissues beyond; or which corrode the body; daprive it of oxygen; or by softening the coverings over ths body (scale insects) cause these to adhere to the plant it is on, killing the insect in any case. The materials of the first group are usually called stomach poisons; those of the second, contact insecticides. The latter could also be used for biting insects but the difficulties in the way of their being successfully applied are such that stomach poisons are used whenever possible. In reaching the insects concerned, either with stomach poisons or contact insecticides, the methods of conveying the material to where the insect is, and of an even and thorough distribution of it are important. Those substances which are solids in the form of fine powders can be blown onto the tree or whatever the insect may be on, but some are liquids. Accordingly, "powder guns" for spreading the poisonous dusts have been used with consideraV^le success, and pumps with a fine nozzle at the end of a line of hose are used for the liquids. 43 44 APPLIED ENTOMOLOGY With stomach poisons, however, the poison is not necessarily eaten by the insect as soon as it falls on the plant, but must or should remain there for some time, as the insects may appear during a period of several days or even weeks. During this time much, probably most, of the poisonous dust would be blown off and the treatment be of little value. In spite of this difficulty, much successful work has been done with dry stomach poisons, and they have many advantages over sprays under certain conditions. It has been found that when stomach poisons are mixed with water and sprayed onto plants in the form of very fine droplets, the spray appearing like a fine mist, each droplet soon dries, leaving behind it the poison it contains, adhering to the leaf, where, unless washed off by rain, it will remain a long time. This has led to the general adoption of spraying, both with stomach poisons and contact insecticides, despite certain difficulties which have developed. STOMACH POISONS Arsenic is the basis of nearly all the commonly used stomach poisons, for though probably more than 50 materials have been tested, only a few have proved at all satisfactory, and with two or three exceptions, useful only under special conditions, they have all been arsenical com- pounds. It would seem natural under these circumstances to use common white arsenic (AS2O3) as the stomach poison, it being, when pure, 100 per cent arsenic (arsenious oxid). But it is found that arsenic dissolves to some extent in water, and that thus dissolved it destroys ("burns") the places on the leaves on which it falls. This result is as bad for the plant as it would be to have the leaves eaten, for the object of spraying is to prevent injury or loss of leaf surface. Because of its solubility in water, therefore, arsenic, as such, is not employed as a spray, but combinations of it with other materials, not, or only very slightly soluble, have been selected for use instead. This produces another diffi- culty. A combination with lead can be obtained for example, which is almost absolutely insoluble in water and therefore entirely safe for use as a spray. But in this material only about one-quarter of it is arsenic, so that an insect, speaking in a general way, would be obliged to eat about four times as much before being poisoned, as would be the case had the material been arsenic instead. By the use of more or less insoluble combinations of arsenic -with other substances, then, reduced injury to the foliage can largely be secured, but a larger leaf surface is consumed by the insect before the poisonous dose is obtained. This is a small matter, however, as compared with the protection of all the foliage on a tree from injury by the spray. Another difficulty in the use of sprays is the weight of the poison mixed in and carried by the water. It has just been pointed out that INSECTICIDES IN GENERAL: STOMACH POISONS 45 the poison must not dissolve, or burning of the fohage will result. The poison, instead, must be suspended in the water, which acts merely as a carrier from the pump to the plant over which it distributes the poison. This distribution should be as uniform as possible in order that all parts of the plant may be equally well protected and covered. If the poison be heavy, settling quickly to the bottom of the pump, uneven distribution will result, some parts of the plant receiving too much of the poison while others will get but little. The best stomach poison from this standpoint therefore, is one which is so light that after mixing it with water it will take a long time to settle to the bottom. The chief stomach poisons now in use in the United States are Paris green. Arsenate of lead. Arsenate of lime. Hellebore, and Sodium fluorid, the last two having only a limited application. Standard formulas for these are given below. Variations from them will be found in connection with the special cases where change from the standard is desirable. Paris Green. — This was probably the first stomach poison used against insects, having been first employed about 1868 for the treatment of the Colorado potato beetle. Chemically, it is a combination of copper, arsenic and acetic acid, containing when pure, nearly 60 per cent of arsenic, which is high as compared with the other arsenicals in use, and this gives the substance its chief value. Paris green has three serious disadvantages. One of these is that some of the arsenic will dissolve in the water it is mixed with, causing injury to the foliage. This can in part be avoided by the addition of lime, which combines with any of the arsenic that separates from its combina- tion with the copper and acetic acid and would cause burning, converting it into arsenite of lime which is only slightly soluble under such circum- stances. Sometimes though, a slight burning takes place, even under these conditions. By Federal law, not over 3 per cent should be soluble. A second disadvantage is that Paris green is a heavy substance, settling quickly through the water to the bottom of the pump, which results in an uneven distribution over the plant. The third disadvantage is that it does not adhere well to foliage, being easily washed off by rains. This means that more frequent sprayings are necessary for the protection of the plants than would otherwise be the case, involving greater cost for material and labor. A standard formula for Paris green is: Per Barrel Per Gallon Paris green , 3-3 lb. 3-^ teaspoonf ul (level) Quick lime 1 lb. 1 teaspoonf ul (level) Water 50 gal. 1 gal. Use fresh stone lime, slaking this in some of the water: work up the Paris green to a paste in a little of the water: add the lime slaked, to the rest of the water, then stir in the Paris green paste. It is not advisable to mix 46 APPLIED ENTOMOLOGY this long before it is to be used, nor to mix more than will be used the same day. Although the addition of lime to the Paris green reduces the danger of injuring foliage, some plants even then, are liable to be burned some- what. Accordingly, the amount of the poison to use per barrel will vary. Thus, for potatoes the Paris green can usually be increased to 3-2 lb. per barrel, while for the peach it is not safe to use more than 3-^ lb. It should not be used on evergreens. Applied as a dust it is usually thoroughly mixed with flour, plaster or air-slaked lime, in about the proportion of 1 part of the Paris green to from 6 to 10 parts of the other, by weight. Paris green is unsafe to apply on stone fruit foliage, and because of the danger of burning in general, it is now less used than was once the case, arsenate of lead having largely replaced it as a spray. Arsenate of Lead. — The value of this material as a spray against insects was discovered about 1892 in the course of the work conducted by the State of Massachusetts on the control of the gypsy moth, and it has now been generally adopted as being, under ordinary conditions, the best stomach poison to use. Two forms of it are available : the basic or neu- tral (ortho) arsenate, Pb3(As04)2 and the acid arsenate, PbHAs04. In pure condition the former is about 25 per cent arsenic oxid and the latter about 33 per cent. The latter is the form in most general use, but on the Pacific Coast, because of local conditions, the former appears to be re- garded with more favor. Arsenate of lead may be obtained both as a paste and as a powder. By law the paste must not be more than half water, but with about this amount present the percentage of arsenic oxid in it is reduced to from 12 or 13 to 19 or 20 per cent. In the powder, water being practically absent, about 32 to 33 per cent is arsenic oxid. As the average in the paste is usually 16 per cent and the price of the powder is about double that of the paste, there is little choice between the two so far as the arsenic is concerned. The Federal law requires that in the paste no more than 0.75 per cent of the arsenic oxid shall be soluble in water. Either form of arsenate of lead shows well on the foliage, which is useful, enabling the sprayer to see parts he has missed in spraying, and to "touch up" those places. It is also very Hght, settling slowly in the pump. Under most conditions arsenate of lead does not burn the leaves, being in fact, the safest of the stomach poisons in this regard, and it adheres to the leaves longer than the others (stomach poisons). On the other hand, it acts slowly on insects because of its rather low arsenic content As a pound of the paste is approximately one-half water, it is necessary in spraying a given area to use twice as much (by weight) as of the powder, in order to supply equal amounts of the poison. INSECTICIDES IN GENERAL: STOMACH POISONS 47 A standard formula for arsenate of lead is: Per Barrel Per Gallon Arsenate of lead paste 3 lb. 3 teaspoonfuls (level) Water 50 gal. 1 gal. Arsenate of lead powder 1}.^ Ih. 9}4 teaspoonfuls (level) AVater 50 gal. 1 gal. In mixing the paste it is w^oll to add some water antl stir thoroughly before adding the rest of the water, in order to get a more uniform mix- ture. If it is allowed to dry it will not work up well thereafter by adding water, and it is also injured by freezing. Arsenate of Lime. — This substance has come into use since about 1914, because of the rapidly increasing cost of arsenate of lead. It is Ca3(As04)2 and may be obtained, like arsenate of lead, either as a paste or a powder. The former contains about 18 per cenj: of arsenic oxid, and the latter about 44 per cent, thus being slightly higher in paste form, and considerably higher in powder form, than arsenate of lead. As the costs of the two forms differ correspondingly, there is little choice between them from this standpoint, but convenience and other factors give a slight preference to the powder. Being stronger than arsenate of lead, less needs to be used in order to supply an equal amount of poison to a given area. Arsenate of lime is not safe for use on foliage, and particularly that of stone fruits, unless an excess of lime is present. Accordingly, as was the case with Paris green, lime must be added to the mixture. A standard formula for arsenate of lime is: Pek Baruel Per (Jallon Arsenate of lime paste 2 lb. 13'2 teaspoonfuls Quick lime 2 to 3 lb. 2 teaspoonfuls Water 50 gal. 1 gal. Arsenate of lime powder ^i lb. 4f^ teaspoonfuls Quick lime 1 lb. 9 teaspoonfuls Water 50 gal. 1 gal. The quick lime, which should be fresh stone lime, is slaked in some of the water, then added to the rest, and the arsenate of lime thoroughly stirred in. While this material is cheaper than arsenat(i of lead and perhaps kills a little more quickly, it has not been in use long enough to be certain just what results may be expected in all cases. At least it may at the present time be termed a very promising insecticide. Poison Baits. — These are included here, as, in most cases at least, they contain an arsenical poison. They are used mainly for the control of cutworms and grasshoppers. There are several formulas proposed. 48 APPLIED ENTOMOLOGY but those consisting of bran or horse manure, poisoned with arsenic or Paris green, and made attractive to the insect by adding strong-smelhng molasses (syrup) and the juice of citrus fruits, have in general been the most successful. Detailed consideration of them will be given in con- nection with the insects for which they are used. Hellebore. — This is the powdered roots of the plants Veratrum album and Veratrum viridis. It is a mild stomach poison and can therefore be usad with safety to man, on plants soon to be gathered for food, as it loses its strength quite quickly on exposure to the air. It is sometimes difficult to obtain fresh. It may be dusted over the plants, sticking on best if applied while dew is on them, or it may be mixed with from one to three times its bulk of flour or plaster, for this purpose. It may also be used as a spray by steeping an ounce in a quart of water and then adding another quart of water. At the rate of half a pound in 10 gal. of water it is effective against house-fly maggots in manure piles. It is too expensive to use except on a small scale. Commercial Sodium Fluorid. — This substance has recently been found to be effective for some insects, acting apparently both as a stomach poison and as a contact insecticide. It is applied as a dust, either pure or mixed in about equal parts, with flour or plaster. Details are given in connection with the insects against which it is used. CHAPTER VIII CONTACT INSECTICIDES For insects which do not feed upon solid food, stomach poisons are useless, and sprays which come in contact with, and kill them in one or another of the ways already indicated, must be used. This is unfortunate for it means the most thorough kind of work if all the insects are to be reached by the spray. It is among such insects too, that the greatest difficulties in accomplishing this, occur. Some, though large enough to be almost certainly reached by the spray have a particularly thick outer shell: others are exceedingly small and thus can find protection under buds, in crevices of the bark and in other places where the spray may not reach them: still others form protective coverings (scales) over them- selves, which fit tightly to the objects they may be on, so that a successful spray must be very strong and penetrating: and finally, many of the smallest and also of the scale-protected insects have marvelous powers of increase, so that if even a single individual escapes treatment, a few days or a week or two will find the plant again swarming with these insects. Every insect therefore, which can be killed by a stomach poison is best controlled by such materials. For the others, oils, soaps, nicotine, sulfur compounds and a few other substances of minor importance serve as contact insecticides. Considering the oils first, there are several which are of use. Among mineral oils, crude petroleum and kerosene are destructive to insect life but so dangerous to plants when of full strength, that some method of dilution becomes necessary. Kerosene Emulsion: standard formula: Common laundry soap ^2 lb. Soft water 1 gal. Kerosene 2 gal. Dissolve the soap in the water (best by shaving it into hot water) : then add the kerosene and with a small hand spray pump having a fine nozzle, draw the mixture into the pump and out through the nozzle back into the dish from which it was drawn. In a few minutes it should become creamy and then begin to thicken. When it has become so thick as to go hard through the pump, this process has been completed, 4 49 50 APPLIED ENTOMOLOGY giving a Stock Solution in which the oil, broken up into very tiny droplets, will not run together again and the water can dilute the mixture. For use against soft-bodied insects, 1 part of the Stock Solution is mixed with about 9 parts of water to spray, while for tougher insects, 1 part is diluted with 4 or 5 parts of water, though this strength may sometimes injure the plants somewhat. The Stock Solution, if well prepared, should keep before breaking down (shown by a film of oil appearing on the surface) for at least a month or two. If the materials fail to thicken in the pump it is probably because the water is "hard water." In that case add a little borax or soda to soften it. Crude Petroleum can be used in place of kerosene in preparing this emulsion, provided the right grade can be obtained, but this is often difficult, and so is not frequently done. Miscible Oils. — These are stronger than kerosene emulsion. They contain mineral oils, a small amount of vegetable oil, naphthaline in some cases, some alkali, and water. Properly made they dilute readily with water. A number of brands of miscible oils are on the market, prepared mainly as sprays for the control of scale insects. For winter use against scales they are generally diluted at the rate of 1 part of the oil to 12 to 14 parts of water. When used in summer against plant lice the dilu- tion should be about 1 part to 35 to 40 parts of water. The material should not be used if free oil stands on it, as this shows that it has broken down and is not safe on the plants. If sprayed on trees in freezing weather it may gather and freeze in cracks of the trees, in- juring them. It is easy to handle and spreads readily from where it strikes, covering more than would otherwise be the case, but it has been claimed, with considerable evidence to support it, that repeated treat- ments with miscible oils cause a cumulative injurious effect on trees. Among soaps, common laundry soap and whale-oil (generally fish-oil now) soap are the usual materials used as insecticides. Whale-oil Soap. — This is a soap made by combining fish oil with an alkali, preferably potash. It is usually diluted at the rate of 1 lb. to 5 or 6 gal. of water to apply against plant lice and similar soft-bodied insects in summer, but is also a fair winter application for scale insects, at the rate of 2 lb. per gallon of water, though more costly than other, equally good materials. Common Soap. — This is a fairly good material at the rate of 1 lb. in 3 to 5 gal. of water for summer use against plant lice and other soft- bodied ir^sects but is not as effective as whale-oil soap and is mentioned only because the latter cannot always be obtained. Nicotine. — This is an alkaloid which occurs in tobacco. It can be obtained by soaking tobacco stems in warm water till a dark brown liquid containing nicotine is obtained, and this is of some value as an insecticide. CONTACT INSECTICIDES 51 Tobacco dust is also used around plants as an insect repellent as well as a fertilizer. Nicotine obtained as above indicated, is varia})le in its strength and the amount it should l)e diluted for use is uncertain. It is also quite volatile and this is a disadvantage when it is used as a spray. Com- mercial nicotine compounds on the market avoid these difficulties by- supplying a material containing a fixed percentage of nicotine combined with sulfuric acid, known as nicotine sulfate 40 per cent. This can be diluted to the proper strength with accuracy, and does not pass off into the air rapidly. Nicotine uncombined, of the same strength, can also be obtained, but should be used for fumigation and not as a spray. Nicotine sulfate is an excellent material to use for plant lice and other delicate insects. It is generally diluted at the rate of 1 gal. to 800 or 1,000 gal. of water, and in some cases a greater dilution even, than this is possil:)le. Sometimes dilution at the rate of 1 to 500 is desirable. Standard formula for nicotine sulfate 40 per cent, 1 part to 800 of water: Per Barrel Per Gallon Nicotine sulfate, 40 per cent J-2 pint 1 '-4 tcaspoonfuls Soap 2 to 3 lb. 1 oz. Water 50 gal. 1 gal. Three-eighths of a pint in 50 gal. of water, or 1 teaspoonful in a gallon, gives nearly a dilution of 1 to 1,000. The addition of soap causes the material to spread more and adhere better. Among the various sulfur compounds, those with lime have thus far been found to be the most successful. Lime-sulfur Wash. — This is prepared by boiling lime and sulfur together in water. Several substances are produced by this boiling, but apparently its insecticidal value is determined by the quantity of calcium polysulfids (CaSi and CaSs) and possibly the calcium thiosulfate (CaSoOs) which are formed in the mixture. The wash can be made at home but it is generally easier to buy it in concentrated form and dilute as needed. It will vary in specific gravity in different cases, and its reading must be taken (a Beaume hydrometer is generally used for this purpose) in order to dilute it properly. The range in readings of differ- ent lots may vary as much as 5° or more, but is usually about 33°Be. Thus, a sample of this density should have 634 gal. mixed with 43^ gal. of water to be of the proper strength for use as a winter spray for the San Jose Scale, when this insect is dormant; while if its density is 30°Be., 7 gal. should be mixed with 43 gal. of water. Tables of density, Beaum6 readings, and the amount of concentrate to add to water to make a total of 50 gal. of spray, both for winter use and as a foliage spray in summer, can be obtained by applying to any state experiment station or to the U. S, Bureau of Entomology. 52 APPLIED ENTOMOLOGY The Lime-sulfur wash is used both as a strong spray against insects during their dormant season, and as a weaker one for general purposes during the summer. In the latter case, besides being a contact insecti- cide, it has a little value as a stomach poison. It cannot safely be used on stone fruits or potatoes, however. This material must be kept in air-tight containers as it decomposes on standing when exposed to the air. A film of some vegetable oil over it, for partly filled containers, will give this protection. It should not be allowed to freeze. For stone fruits where a summer treatment seems necessary, self- boiled lime-sulfur may be used. This is. prepared by slaking 8 lb. of fresh stone lime in a barrel, in enough water to nearly cover it. Eight pounds of fine sulfur should be gradually added to this, as soon as the lime begins to slake, running the sulfur in through a sieve to break up any lumps. This mixture should be constantly stirred and more water added to form first a thick paste, then gradually a thin one. The heat produced by the lime in slaking will cause the mixture to boil for several minutes. When slaking is at an end, cool the mixture rapidly by adding considerable water, then strain into the pump to remove lumps of lime, but working any lumps of sulfur through the strainer; then dilute with water to a total of 50 gal. Dry Sulfur Compounds. — These substances have recently appeared in competition with the lime-sulfur wash, the advantages claimed for them being ease of handling, reduction of shipping charges, no deteriora- tion on standing, and equal efficiency at lower cost. These substances are sulfid combinations with either potassium, sodium, barium or calcium. The amount of sulfur present varies greatly in different brands. They do not contain as much of the polysulfids which appear to be the actual insecticides of the lime-sulfur wash as the liquid wash, and even the amount of sulfur present in them, after the addition of water according to directions, is less than in an equal quantity of the wash, so that basing efficiency on the amount of sulfur, regardless of its form, the amounts of these dry materials would have to be greatly increased to equal that of the wash, and would therefore seriously increase their cost. At the present time their value cannot be considered as having been finally settled though in many cases field tests of them have given good results. Continued studies and tests of these materials are needed to determine their real value. Sulfur. — This substance in the form of a very fine powder, can be dusted over plants for the destruction of red spiders and other mites, or it may be made into a paste with soapy water, using 10 lb. of sulfur and 2 lb. of soap in 50 gal. of water, and applied as a spray Its use is rather limited and its actual value somewhat questionable in many cases. CONTACT INSECTICIDES 53 Pjrrethnim, Insect Powder or Buhach. — This is made by grinding up the blossoms of certain plants, which contain an essential (and volatile) oil effective against insects but not injurious to man. Its use is mainly limited to small areas, and best, those which can be tightly closed. Various other materials will be considered in connection with the particular insects, for the control of which they are used. CHAPTER IX INSECTICIDES AND FUNGICIDES: FUMIGATION COMBINATIONS OF SPRAY MATERIALS The greater part of the cost of spraying comes from the time and wages of the workers, the materials used being rather inexpensive in comparison. Wherever it is possible therefore, to make two or three applications at once by using combined sprays, the cost is much reduced. Frequently there are cases where the application of a stomach poison for chewing insects and of a contact insecticide for sucking forms, can be made at about the same time. Treatment for fungous diseases may also be desirable, and a satisfactory mixed spray for all three purposes can often be given. Certain precautions must be taken in mixing sprays, however, as in some instances the materials of two or more sprays, when combined, will undergo changes, producing substances injurious to the plant or affecting the value of the spray for the purpose for which it was intended. No spray material containing soap should be combined with one con- taining lime, as when these materials are brought together, a calcareous and insoluble soap is formed. Thus, when nicotine sulfate is used with lime-sulfur or Bordeaux mixture, the soap usually added to the former must never be put in. Arsenate of lead and compoands containing sodium or potassium sulfid, when mixed, produce sodium or potassium arsenate which is very soluble and will injure foliage, so this combination should also be avoided. Bordeaux mixture, a fungicide, combines well with most of the insec- ticides except those containing soap, but as it contains lime, an insec- ticide with soap is not safe for this combination. In most cases the Bordeaux mixture ready for spraying can be regarded as an equivalent amount of water, to which to add the insecticide. For example, in combining Bordeaux and arsenate of lead, simply add 3 lb. of the paste to 50 gal. of the Bordeaux. Bordeaux mixture will safely combine with any of the arsenical poisons given in this book, and also with nicotine sulfate if the soap be omitted. Lime-sulfur at summer strength may be used with arsenate of lead or nicotine sulfate, leaving out the soap, though in the former case a decomposition is liable to take place which reduces the value of the material. Lime-sulfur at winter strength when added to the 54 INSECTICIDES AND FUNGICIDES: F I'M 1(1 AT ION 55 arsenate of lead brings about a decomposition, as a result of which con- siderable soluble arsenic is formed, and the efficiency of the lime-sulfur is also reduced about one-third. This may be avoided, however, by slaking 5 lb. of quick lime and adding this to the lime-sulfur before putting in the arsenate of lead. Lead arsenate can be combined with nicotine sulfate, and in some cases at least, with kerosene emulsion. With soap, acid lead arsenate decom- poses to some extent forming a solu))le arsenate which is dangerous on foliage. Small amounts of soap added as a "sticker," however, are often advantageous even in spite of this decomposition and are frequently recommended, the gain by the addition of the soap being greater than a small injury by burning. FUMIGATION In theory, fumigation is the best method for the control of insects. A gas will reach every portion of a room or a plant, penetrating where no spray can reach, so that insects no matter how well concealed in crevices, under bark or in other locations, will be reached. Still, practical diffi- culties in the use of poisonous gases are numerous and result in a restricted use of this method of treatment. The gases used for the destruction of insects act either as actual poisons which enter the body through the tracheal system and directly attack the tissues, or combine with the oxygen of the air and thus remove it from availability by the insect, which suffocates in consequence. In either case, successful fumigation depends upon the liberation of a suf- ficient quantity of the gas or vapor to make it strong enough to kill the insect. This at once eliminates trees, bushes and crops growing out of doors from consideration, unless they or their products are so valuable as to make the use of gas-tight tents to cover them during treatment worth the expense, which is considerable. Accordingly, fumigation is generally made use of only with citrus trees, and in houses, greenhouses or other places capable of being tightly closed. Under the conditions mentioned, however, it is an excellent method for insect control, though where plants are to be fumigated, it is usually done at night as the gases or vapors are less liable to cause injury then. The fumigants most often used are carbon disulfitl, nicotine, sulfur and hydrocyanic acid gas. Carbon Disulfid (CS2). — This is obtained in liquid form but becomes a gas on exposure to the air. Impure grades are as good for fumigation as the purified article. The number of cubic feet in the space to be fumi- gated is calculated, and in general from 10 to 20 lb. of the disulfid are used for each 1,000 cu. ft., though if the place is very tight, less than this will be needed. As the gas is considerably heavier than air, the usual OfS AFMJED EyrOMOtJOGT ptaenee ie 7«: r«rr lie 3^-:di ii ' ii^bes dose to the top of the pbee to be f:z=ii^;:ai. ikS 7^^^ r. ~ 7 zrMwe lapidlv in sodli fi 7r7TfTtSTT,E fades vitb ditR i icnl . . zn ^^ eveKBg. eostinaed d n^it, and S__.: — -Jiizr ac a. I i wmgtwt is prohah^ doe botii to its _dh Ae OTTx^ ^ ^fe sir. ^-ninating the and F." -^it-affldtotheic: --• ~ ■ : apfasonoos^BS. ii ^ ^2^^ wHBBg -Tin n li^ ^'rb^^ lo bc fomigated, and K ^>e ^spfcoin _ so in greenlaoases b e tnwM oopBL It rmMmnf Ije sbMy -:s&d with Mring plants. Fran 1 to 2 Ih. of sidfiir per lJflQOen.^CL' :.antit3r teed. Pofehed Metal gndaaces in idhe place t : . ^sone t a i wij Ja' d b^ the g^e, and these dnrid be lenoved. as weft as coined goods vhidi aie hiparhed by it. Ifesal es& be psoteesed hr etncsiag it withTaaefineL Tht ^^mcral ptaeoee k to plaee a lai|§t iron kettle on backs to keep it eS the- Soer. wticfe m that place iilaiidil be covered for a «figtawy of BgK wisk :mpiiwi ihiw|i^ vhick «9 not be i^med or binned if the ^siftas over. Li the kettde place the aid^ir and add to it a fitde tSSECTICJDES AXD FVSGICIDES: FTMKATJOX 57 denstored afeofaol to ineore barning: tiieii figitt the mM-^r ^aad loeep tfe place t%iith- dosed for 24 to -IS lir.; tfaea air thorougilj. HydiucjaM c urid Gas i^CX . — ^Thk k one of tke moei pomahA aad dai^aoiB gases known, and p&gso^g having had no tiaiMa g in its ice arc advised not to trv it. It k prodastd hy the adifitioB ears to be largely replaced there, by the Cahfomia Grape-root worm {Bromine obscuru.s L.). The insect passes the winter as the nearh^- or full-grown lar^^a, a number of inches deep in the ground, but in spring it comes nearer the surface and feeds on the roots of the grape imtil full grown. Pupation usually occurs two or three inches below the surface and the adult beetles begin to emerge about the time blosso min g of the grape ends, most of them appearing during a period of 4 or 5 weeks. The beetles (Fig. 117) are brown, covered with whitish hairs ; are rather stout, about a quarter of an inch long and have long legs. They feed on the grape leaves, making irregular holes, often so connected as to form narrow, crooked shts. The eggs are laid, several hundred in aU, placed in clusters of about 30 or 40, mainly under loose strips of bark. These hatch in about 10 days and the tiny grubs drop to the ground and work down to the roots consuming the smaller ones entirely and burrowing in the larger ones, until winter, when they are full grown or nearly so. When these insects are abundant the grape vines may be killed in a year or two but the usual result of their presence is to so check the growth of the plants that httle or no crop is obtained. The grape-raising territon,^ of western New York, Pennsylvania and Ohio appears to suffer most from the attacks of this pest. 126 APPLIED ENTOMOLOGY Control. — The adult beetles can be killed by spraying the leaves with arsenate of lead using 3 or 4 lb. of the paste in 50 gal. of Bordeaux mixture, just before or as soon as the first signs of feeding appear, and again after 10 days. Great care must be taken, however, to do this work thoroughly, as the beetles avoid sprayed foliage. The beetles may also be jarred off the vines, particularly on warm days, onto sticky boards, fly paper, or sheets or some other type of catcher placed beneath the plants, whence they can be gathered and destroyed. The pupae are located within a few inches of the top of the ground and are mostly within two or three; feet of the vine. In this state of their existence they are easily destroyed by any thorough breaking up of the soil where they are, and this is taken advantage of by throwing up the earth on each side of the vines in the fall to form a ridge. Most of the larvae work up into this to pupate, the following spring, and while the insects are in the pupa stage there this ridge should be hoed ■ away by a horse-hoe and by hand, or by the latter alone for small areas. Later cultivation will reach some of those escaping the first treatment which in the grape belt named is usually about the middle of June. The Calif ornian species is a Httle smaller than the one just described, and jet- black or brown. Its habits and methods for controlling it are about the same as with the eastern pest. The Elm Leaf Beetle {Galerucella luteola Muls.). — This European insect appears to have reached this country at Baltimore about 1834 and has now spread through most of the New England and Middle Atlantic States and westward nearly to the Mississippi River, though not everywhere present within these limits. The adult beetle (Fig. 118) is about a quarter of an inch long, dull yellow in color, with black spots on the head and pronotum, a black band near the outside of each elytron, and a short streak at the base of each, nearer the middle. The beetles winter over in protected places and in the spring the dull yellow has changed to an olive-green (Fig. 118). They fly to the elm trees when the foliage develops, and feed, eating irregular holes in the leaves and from time to time lay- ing yellow eggs on the underside of the leaves, usually about 25 in number and nearly always in two rows, side by side (Fig. 1,18). The eggs hatch after about a week and the tiny yellow and black grubs feed for about 3 weeks, working on the under surface and leaving the upper epidermis of the leaf unbroken. When full- grown (Fig. 118) and about half an inch long they crawl down the tree to the trunk and pupate for from 1 to over 3 weeks according to the temperature, either in crevices of the bark on the lower part of the trunk or on the ground near the foot of the tree (Fig. 118). In the more northerly states the larvae feed during June. Farther south they begin in May and a second generation feeds during the late summer or early fall. The European elms are most severely injured by this insect but other species often suffer greatly. Control. — ^Spraying the trees about the time the eggs are laid, i.e., soon after the leaves are fully grown, with arsenate of lead is the usual method of control. The strength of the material should be increased above the standard to 5 lb. of the paste, to obtain good results, and it should be kept in mind that as the grubs do not feed on nor reach the upper surface of the leaves, the spray shoald be directed as far as possible onto the under surfaces. THE COLEOPTERA 127 Fig. 118. — The Elm Leaf Beetle (Galerucella luteola Muls.) : 1, egg clu.stefr; la, single egg greatly enlarged; 2, recently hatched larva (grub); 3, fxill-grown larva; 4, pupa; 5, beetles after wintering over; 6, freshly emerged beetles; 7, under surface of leaf showing grubs, their work and a few holes eaten by adult beetles; 8, leaf nearly skeletonized by the larvae; 9, leaf eaten by adults. Hair lines by Figs. 1 to 6 show natural size: 7, 8 and 9 natural size. {From Bull. 332 Ohio Agr. Exp. Sta. After Felt.) 128 APPLIED ENTOMOLOGY Fig. 119.— Tortoise Beetle {Deloyala clavata Fab.) about 2^ times natural size. (Original.) Destroying the descending larvae and the pupse on the lower part of the trunk and on the ground, with a strong kerosene emulsion spray is an auxiliary treat- ment, but as these individuals have completed their feeding, this affects only the- abundance of the next generation. Power sprayers are a necessity for spraying tall trees in the way here described. The Tortoise Beetles are interesting members of the Chrysomelidae (Fig. 119) because of their resemblance in form to tortoises and inmost cases, on account of their golden color, which is lost after death. Some species attack the sweet potato but are not usually serious pests. They are small insects, usually not over a quarter of an inch long, nearly as wide, and often with black mark- ings. If they become injuriously abundant, spray- ing the leaves on which the larvae feed, with arsenate of lead will control them. Family Bruchidae (Pea and Bean Weevils). — In this group of small beetles the head is extended downward into a broad but short snout. The elytra are shorter than the body leaving the hinder end of the abdomen exposed above. The larvae feed in the seeds of leguminous plants such as peas and beans, and frequently cause a great amount of damage. Several kinds are abundant in the United States, the pea weevil and the common bean weevil being perhaps the most important. The Pea Weevil {Bruchus pisorum L.). — This pest of field and garden peas winters as the adult beetle (Fig. 120a) either in peas or in protected places, and after the pea pods begin to form, lays its eggs on them. It is about one-fifth of an inch long, brownish, with black and white spots. The larvae (Fig. 1206) bore their way into the peas, the holes they make either closing up or being too small to be noticed, and feed on the contents of the pea until full-grown. They then pupate (Fig. 120c) and upon the pro- duction of the adult, those in the South leave the peas, while in the North they remain in them over winter. Only one weevil usually feeds in a pea and the insect cannot reproduce in dried peas. There is there- fore only one generation a year except where spring and fall crops of peas are grown. Fig. 120. — Pea Weevil (Bruchus pisorum L.) : a, adult beetle; h, larva (grub); c, pupa. Greatly enlarged. {From U. Bull. 983.) S. D. A. Farm. THE COLEOPTERA 129 The Common Bean Weevil (Bruchus obtectus Say). — This insect is now found in nearly all parts of the world. The beetle is smaller than the Pea Weevil and is brownish-gray in color, its elytra slightly mottled (Fig. ] 21). The beetle lays its eggs on or in the pods of the beans growing in the field, either in holes made, or in cracks caused by the pods splitting. In the case of shelled beans the eggs are placed on the beans themselves. The larvae gnaw their way to and into the beans, and unlike the Pea Weevil, a number may enter the same seed and feed upon its substance. Devel- opment from the egg to the adult occurs within the bean and the adult finally escapes through a circular hole it has cut in the skin after having spent from 3 weeks to nearly 3 months there, according to the tempera- ture where the beans are kept. When infested beans gathered in the field are brought in, their infestation may not be apparent, but after being kept a while, the adult beetles will escape Fig. 121. Fig. 122. Fig. 121. — Adult Common Bean Weevil {Br^^chus obtectus Say), greatly enlarged: hair line at right shows real length. (From U. aS. D. A. Farm. Bull. 983.) Fig. 122. — Work of Bean Weevils, natural size. (Original.) and lay their eggs for another generation which will develop in the same seeds if these are kept where it is fairly warm (Fig. 122), and thus by spring there may be practically no beans left to plant. Six generations may be produced in a year in the South and if the beans are kept where it is warm during the colder months, as many may occur in northern localities, though in the field it is doubtful if there are more than one or two. Another species, the Cowpea Weevil (Bruchus chinensis L.) which feeds on the cowpea, and other peas, and beans, is more abundant in the South, and a fourth, the Four-spotted Bean or Cowpea Weevil {Bruchus quadrimaculatus Fab.) has a wide distribution, probably wherever cowpeas are grown. Both of these species breed generation after generation in stored cowpeas, and in warm temperatures there may be a number of generations each year. The Broad Bean Weevil {Bruchus rufimanus Boh.) in its life and habits more nearly resembles the Pea Weevil than the other species above considered. It is injurious in Europe and Northern Africa and has now established itself in Cali- fornia. The beetles resemble the Pea Weevil but seem to prefer broad beans or horse beans. They appear in the fields in March and lay numbers of eggs on the bean pods and the grubs on hatching make their way to the young beans, several 9 130 APPLIED ENTOMOLOGY often entering one bean. Feeding is completed by early August and the adults are produced later in the fall. They generally winter in the beans but do not breed in dried beans, there being therefore only one generation a year. Injuries. — The damage caused by the attacks of pea and bean weevils is of two kinds: injury by consuming the bulk of the seed and leaving the remainder unfit for food; and injury by so reducing the stored material or the germ itself that the seed cannot germinate and grow. Control of Pea and Bean Weevils. — The original attacks of these in- sects are upon growing plants out-of-doors. Here no. control seems pos- sible. When the crop is gathered, however, treatment can easily be given by shelling at once, placing the seed in gas-tight receptacles, and fumigating it with carbon disulfid, using this at the rate of at least 8 or 10 lb. for every 1,000 cu. ft. of space in the container, and continuing the treatment for at least 1 — better 2 — days. The disulfid may be poured di- rectly onto the top of the seeds. For best results this should be done in a place where the temperature is at least 75°F. Then the seed should be packed in weevil-tight boxes, but it would be wise to examine it again after a time and if living weevils are still present, give it another treat- ment. Where the seed is not to be used for food, packing it in air-slaked lime at the rate of 1 part by weight of lime to 2 or 3 parts by weight of seed has proved satisfactory. Even where use as food is intended, this method can be used if the seed is thoroughly washed before cooking. Cold storage below 34°F. will prevent development of the insects. Heat will destroy the weevils and if seed is raised to 131°F. and kept at that temperature for an hour, this will kill all the weevils present. Appar- ently, treatment in this way and for this length of time will not prevent germination. None of these methods will prevent reinfestation if the seeds are afterwards exposed to attack by insects from outside, where the temperature is such that they are active. In general then, give the first treatment immediately after gathering, and store in tight containers and preferably in a cold place. The shorter seasons and cold winters of the North give the pea and bean weevils less opportunity to increase through a number of generations than in the South, and many of the adults are killed by the cold. North- ern climates for these reasons are therefore better for the extensive pro- duction of seeds of these plants. Family Cerambycidae (Round-headed Borers or Longicorn Beetles). — The insects of this family are for the most part of fair size, a number being several inches in length. Their antennae are usually long — sometimes longer than the body — and the beetles are frequently bright-colored and strikingly marked (Fig. 123). The larvae are chiefly wood-borers, living in burrows in the trunks or roots of trees, or the pith of plant stems, and are termed round-headed THE COLEOPTERA 131 borers because the thoracic segments are circular in outline and the tunnels they produce are therefore also of this shape. The larvae them- selves are soft, whitish or yellowish grubs, with strong jaws, and most of them have no legs. The eggs are usually laid on the bark of the tree and the larvse live on the wood they tunnel out, for a varying period, usually 2 or 3 years, and pupate in the tunnels just beneath the bark, through which the emerging beetle finally gnaws its way and escapes. Fig. 123. — Cerambycid {Monohammus), natural size, showing long antennae. {Original.) Some species cut the stem in which they live, nearly through, and when it breaks off, fall with it to the ground, thus pruning the tree. Those which tunnel in the heart-wood of timber trees often greatly reduce the value of the timber by their holes. Some species attack sound wood and apparently vigorous trees, while others seem to prefer trees already un- healthy, for their food. The family is a large one and contains many forms injurious to shade and forest trees. The Round-headed Apple-tree Borer {Saperda Candida Fab.). — This serious enemy of the apple tree is found practically everywhere in the eastern United States except in the extreme South, and westward into Minnesota, Iowa, New Mexico and Texas. It also attacks the service tree, pear, quince, thorns, mountain ash, and a few other Rosaceae. The adult beetle (Fig. 124) is a little less than an inch long, pale brown above, with a pair of white stripes extending backward from the head across the pronotum and along the elytra to their tips at the hinder end of the body. Beneath, it is silvery white. It appears during the late spring and summer months and lays its eggs singly here and there in small slits it cuts in the bark near the base of the tree, laying about 15 to 30 in all. On hatching, 2 to 3 weeks later, the larva burrows through the bark to the sap-wood, and there makes broad, rather shallow galleries just under the bark and in general working downward. The bark over these gal- leries frequently dries and cracks, or the borer makes holes in it, letting 132 APPLIED ENTOMOLOGY out the borings and castings, often called "sawdust" which shows the location of the burrows. After hibernating during the winter the borer (Fig. 124) resumes its work the following spring, still feeding on the sap- wood, and if the tree is small or if several borers are present, girdling may result. After a second winter in hibernation the borer turns its atten- tion to the heart-wood, boring into this, and finally as it approaches full growth, working its way out toward the surface, being now about three- quarters of an inch long. After a third winter of rest the larva pupates in its tunnel in the spring, having previously carried the tunnel out to the bark, and the adult beetle emerges after about 3 weeks. One generation Fig. 124. — Round-headed Apple-tree Borer {Saperda Candida Fab.) : back and side views of adult beetle on bark and exit hole; full-grown larvse (borers). (After Rumsey and Brookn.) accordingly requires 3 years in which to complete its life history but this comes in parts of 4 calendar years. In the southern part of its range this is shortened to 2 years and in intermediate regions some may require 2, and some 3 years. Small trees suffer most severely by the attacks of this pest, a single borer often entirely girdling a tree : larger ones are weakened and become unhealthy and if strongly infested may also be killed. Control. — Various methods of control have some value. "Worming" the trees, i.e., cutting out the young borers early in the fall is a good practice if it is thoroughly done and if the cutting is carried on carefully. Litter should be carefully scraped away from the trunk to expose any sawdust present, and from this the burrows can be located and the dead bark cut out and the borer killed, either in place under the bark or by running a flexible wire into its burrow if it has gone deeper into the tree. In cases where the borer cannot be reached by the wire, a little carbon THE COLEOPTERA 133 disulfid on cotton placed in the burrow, the opening then being closed with mud, will serve the same purpose. Worming should be done in early fall; the work should be thorough, and host trees of every kind within several hundred feet of the orchard should be worked at the same time for the beetles do not usually fly far and if the immediate neighborhood is cleared of them, reinfestation from a distance does not occur very frequently. Thick paints are sometimes used as repellents. These are applied beginning a few inches below ground, the earth being removed for the purpose, and extending about a foot up the trunk, just before the egg- laying period begins. The paint should be thick and be thoroughly applied and should be pure white lead in raw linseed oil, as other materials have been known to injure the trees. Protectors, such as newspaper wrappings (several layers thick), building paper, cloth, wire netting, etc., may be used, being placed around the trunks before egg-laying begins. In all cases, however, these must enter the ground at the bottom and be tightly fitted around the trunk at the top and be without holes or cracks through which the beetle can crawl. Asphaltum has given fair results in some cases, but appears to be liable to injure the tree. As the beetle feeds somewhat on twigs and leaves, the usual sprayings with a stomach poison for other apple pests are liable to kill some of the beetles also. Woodpeckers feed freely on the borers. Family Coccinellidae (Lady Beetles, Lady Bugs or Lady Birds). — The lady beetles are nearly all carnivorous, feeding both as larvae and adults on scale insects, plant lice and other important pests. They are generally small beetles, nearly circular or oval in outline, strongly convex, often resembling in size and form a split pea. Their colors are usually black and red or reddish-yellow, sometimes the spots or markings being black on a red ground, sometimes the reverse. In a number of species the beetle is entirely black (Figs. 125 and 126). The larvae (Fig. 126) are active and crawl around over leaves, twigs, etc., searching for their food. They are dark colored, but frequently have a few spots of yellow or blue on the side of the body, and their general appearance has suggested to some persons, a resemblance to alligators. The family is quite a large one, and its species are abundant and well distributed over this country. Among the more useful or noticeable of the family is the Two-spotted Lady beetle {Adalia bipunctata L.), one of the smaller species averaging about a sixth of an inch in length (Fig. 1256). The head is black, sometimes with two yellow spots; the pronotum black with yellow side margins, and the elytra are red with a black dot in the center of each. This insect frequently winters in houses and may be found on the windows in spring trying to escape. It is often mistaken for some 134 APPLIED ENTOMOLOGY injurious household pest on this account. This species feeds mainly on plant lice, but to some extent also on the pear psylla. Another species of about the same size is known as the Twice-stabbed Lady beetle (Chilo- corus bivulnerus Muls.)- Here the head and pronotum are black, as are also the elytra, except for a red spot in the center of each, thus just reversing the elytral color pattern of the last described species. It feeds on scale insects and also on plant lice and the Colorado Potato Beetle. Fig. 125. — Examples of Lady Beetles: a, Twice-stabbed Lady Beetle (Chilocorus bivulnerus Muls.) : b, Two-spotted Lady Beetle {Adalia bipunctata L.) ; c, Nine-spotted LadyBeetle (Coccinella novem.notata Hbst.) : d, Spotted Lady Beetle {Coleomegilla fuscilahris Mu)s.): all about twice natural size. {From Conn. Agr. Exp. Sta. Bull. 181.) Other common species are the Nine-spotted Lady beetle {Coccinella 9-notata Herbst.) with nine black spots on its red elytra; the Fifteen-spotted Lady beetle {Anatis 15-punctata Oliv.), the largest species in the Northeastern States, which has 15 black spots on its red elytra; the Pitiful Lady beetle {Pentilia misella Lee), a very tiny black species which feeds on scale insects and aphids, and the Spotted Ijady beetle {Coleomegilla fuscilahris Muls.) about a fifth of an inch long, usually bright pink with black spots and with its body rather oval in outUne, somewhat pointed behind. This species feeds on many kinds of plant hce and other small insects and tends to hibernate in' clusters, often several hundred together, under leaves at the bases of treetrunks. b d a Fig. 126. — Different stages of the Nine-spotted Lady Beetle: d, eggs. All much enlarged. (Modified from Palmer, Ann. a, adult; b, larva; c, pupa; Eni. Soc. Am., vii, 1914.) The Convergent Lady beetle {Hippodamia convergens Guer.) is about a quarter of an inch long, with two converging yellow marks on the pronotum and six black spots on each elytron. This widely distributed species has been found feeding on a number of kinds of plant lice and in addition, on asparagus beetle larvae, eggs of the Colorado Potato beetle and of the Grape-root worm, red spiders, the Bean Thrips, Alfalfa Weevil and Chinch Bug. On the Pacific Coast it gathers in enormous numbers THE COLEOPTERA 135 in the high mountains to hibernate and while thus collected in quantities they are gathered and in spring distiibutcd through the truck-growing regions to attack the plant lice, about 30,000 being regarded as enough to protect the plants growing on 10 acres. Several tons are often collected for distribution for this purpose. It takes nearly 1,500 of these beetles to weigh an ounce. Because of their efficiency as feeders on insect pests, a number of kinds have been introduced into this country to attack the special insects of their native lands which have reached the United States and have become pests here. Among these are the Vedalia (Novius cardinalis Muls.) (See Fig. 216), imported from Australia to attack the Cottony-cushion or Fluted Scale; the Mealy-bug Destroyer (Cryptolcemus montrouzieri Muls.), brought also from Australia to attack several kinds of Mealy-bugs found in California; the Steel-blue Lady beetle (Orcus chahjbeus Boisd.) which feeds on a number of kinds of Armored Scales; and the Black Lady beetle (Rhizohius ventralis Erichs.) which is an active enemy of the Black Scale (Saissetia oleoe Bern.); besides numerous other species. Many of these imported forms have done valiant work in their attacks upon their ancient foes in the country to which both have come, but in some cases this attempt to aid nature in the control of insect pests has been less successful, and it is evident that the success of each experiment of this kind can rarely be determined beforehand. (See Cottony Cushion Scale, Chapter XXVI). Family Tenebrionidae (Darkling Beetles). — This rather large family of beetles contains many forms found on the ground and superficially resembling the Cara- bidsB. They are usually rather slow of movement, however, feed on vegetable instead of animal food, and while their fore and middle tarsi are each composed of five segments as in the Carabids, their hind tarsi each have only four. They are particularly abundant in the Southwest and West, though a number are present practically everywhere. The Yellow Meal -Worm {Tenebrio molitor L.) about three-quarters of an inch long (Fig. 127), is often found around stores of grain, in pantries, stables etc., and its larva which closely resembles a wireworm, feeds upon meal and similar materials. It is often raised as food for cage birds. Where abundant, a thorough cleaning out of infested places, ,^ , ' ^~' 'T^^®'!"^ . „ , , . ' . .,,,,• , ,. ■ . Meal-worm (Te/iebno tollowed by sprmkhng an--slaked nme around, or fumigation molitor L.), about of the infested material with Carbon disulfid, is all that is natural size. (Orig- inal.) necessary. ^ Family Meloidae (Blister Beetles). — The insects of this family also have but four segments to each hind tarsus. The body is quite cylin- drical and rather soft, and the head joins the thorax by a distinct neck (Fig. 128). Many of the members of this family contain a substance 136 APPLIED ENTOMOLOGY called cantharidin, which when applied to the skin, produces blisters. The bodies of these species, powdered, are used in medicine under the name ''cantharides" or ''Spanish flies," for blistering purposes. A dozen or twenty kinds of Blister beetles, averaging from half an inch to over an inch in length are more or less serious pests as adults, feeding during the summer or fall on foliage and blossoms, various vege- FiG. 128. — Adult Blister Beetles: a. Black Blister Beetle (Epicauta pennsylvanica De G.); b, Ash-gray Blister Beetle {Macrohasis unicolor Kby.) ; c, Striped Blister Beetle (Epicauta vittata Fab.) ; all about natural size. (Modified from U. S. D. A. Bulletins.) tables and ornamental plants being attacked. Vegetable crops are sometimes seriously affected. The larvae on the other hand, feed on the eggs of various species of grasshoppers and are therefore beneficial. The adults are not easily controlled as they are rather resistant to arseni- cal poisons, and as they fly freely, it is difficult to reach them with contact insecticides. In cases where stomach poisons can be applied, arsenate of lead, taking about 4 lb. (if the paste be used) to 50 gal. of water, has proved the best treatment. Where this cannot be done, hand- picking, and screening valuable plants with netting, may be resorted to. RHYNCHOPHORA (Snout Beetles) The snout beetles are included in several families. Some are called curculios, weevils, and bill- bugs, and those of one family, the larvae of which work in the bark and wood of trees, are called Engraver beetles and also bark borers. Over twenty-five thousand species of Rhynchophora are known (Fig. 129). Except for this last named famfly, most snout beetles feed on fruits, nuts, etc., though a few attack stems and leaves. The white, nearly always footless larvae, also feed for the most part on such materials, and a number are very destructive and therefore important pests. Fig. 129. — Examples of adult Snout Beetles showing differences in the develop- ment of the snout. About twice natural size. {Original.) THE COLEOPTERA 137 The Plum Curculio (Conotrachelus nenuphar Herbst). — This Insect is a native of the United States and formerly fed upon the wild plum and thorn fruits, but now also attacks cultivated plums, prunes, cherries, nectarines, apricots, apples and peaches. It is found practically every- where east of the Rocky Mountains, though in the western portion of this area it seems to be of less importance than elsewhere. The adult beetle (Figs. 130 and 131) is small, being only about a Fig. 130. Fig. 131. Fig. 130. — Adult Plum Curculio (Conotrachelus nenuphar Hbst.), view from above. About five times natural size. (Modified from U. S. D. A. Bur. Ent. Bull. 103.) Fig. 131. — Side view of adult Plum Curculio showing humps on the back. Enlarged about five times. (Modified from U. S. D. A. Bur. Ent. Bull. 103.) fifth of an inch long, dark colored as a whole but mottled with gray and brown. Its elytra are rough and on each is a black, shining hump a little behind the middle. This pest spends the winter, or the colder months in the South, hiding in any protected place it can find, particularly in the woods, in stone walls or under leaves. It appears about the time the plum buds open in spring and feeds more or less on the developing leaves. When the fruit begins to develop, the beetles turn their attention to it, feeding by cutting a circular hole through the skin and consuming the flesh beneath to a depth about equal to the length of the snout of the insect. They also begin now to lay their eggs in the young plums, cutting a hole in the skin and then running the snout ob- liquely into the flesh beneath. In this cavity the egg is placed and it is then pushed farther in by the snout. The beetle next cuts a crescent-shaped slit through the skin close to the egg (Fig. 132) and carries this down through the flesh beneath the egg which thus comes to lie in a sort of flap which wilts and remains soft, and the crushing of the egg by the growth of firm tissue there is prevented. Fig. 132. — Egg puncture and feeding puncture of Plum Curculio in young plums. (From U. S. D. A. Farm. Bull. 90S.) 138 APPLIED ENTOMOLOGY Several hundred eggs are laid in this way and the "spot and crescent" marks of the insect on small plums are familiar to plum growers. The fruit often pours out gum at these places, probably in an attempt to repair the injury. The eggs hatch in a week or less and the tiny whitish grub bores through the flesh, and in stone fruits passes to the stone, around which it feeds for about two weeks or until full-grown. It then leaves the fruit, and as this in most cases has fallen before this time because of the injury, the larva finds itself on escaping, on the ground. Into this it now burrows an inch or two and pupates. About a month later the adult beetle emerges, comes to the surface of the ground and attacks fruit for food, egg- laying rarely if ever taking place at this season, and when cold weather comes on it locates in some protected place for the winter. There is accordingly, but one generation a season. Fig. 133. -Apple showing injury by Plum Curculio in fall. Sta. Bull. 98.) {^^odified from III. Agr. Exp. This insect, both by its feeding and egg-laying punctures, affects the value of the fruit not entirely destroyed, not only in appearance but by the opportunity these cuts afford for the entrance of the spores of disease-producing fungi, and the destruction in the United States which it causes has been estimated at over eight million dollars annually. While the insect rarely succeeds in developing in the apple, the punctures cause dropping of the fruit or its malformation, and the production of hard, woody places in the pulp. In the fall its feeding holes in apples also cause much injury (Fig. 133). Control. — No one method nor even all the methods of control taken together will give entire freedom from this pest. A combination of i THE COLEOPTERA 139 treatments, however, will accomplish considerable in this line. The usual measures taken are as follows: (1) Remove all opportunities for the successful wintering of the adults, as far as possible. Rubbish, stone walls, and trash of all sorts should be removed. Plum orchards near woodland are poorly located from this standpoint. (2) The curculio prefers shade in which to work, and larvae even inside fallen fruit are unable to survive any long exposure to direct sunlight. The trees therefore should be so pruned as to let the sunlight through all parts, and fallen fruit should be exposed to the sun by proper treatment of the ground under the tree. (3) Fowls and hogs will eat many of the larvae in the fallen fruit and larvae or pupae in the ground, and should be allowed to run under the trees; or thorough, shallow cultivation under the trees should be given from the time the larvae begin to leave the fruit until at least 6 weeks later, to destroy the insects there. (4) Spraying with arsenate of lead either alone or combined with the self-boiled lime-sulfur has been fairly successful if the applications be thorough and at the right times. For plums spraying with 2}^^ lb. of lead arsenate paste (13-^ lb. of the powder) in 50 gal. of water or lime- sulfur as soon after the blossoms fall as leaves begin to develop, and the treatment repeated 8 or 10 days later has proved the best method. Cherries can be treated in the same way. With peaches, 2 lb. of the arsenate in 50 gal. of water, to which the milk of lime obtained by slaking 2 lb. of quick lime has been added, is sprayed as soon as the "shucks" are beginning to shed from the blossoms. About 3 weeks later a spray of 2 lb. of the arsenate in 50 gal. of the self-boiled lime-sulfur is made. A third treatment about a month before the fruit begins to ripen, using the lime-sulfur only, is also often given. • For apples the precautions neces- sary in spraying stone fruits with arsenate of lead need not be taken. Here the treatments commonly given for the Codling Moth (see Chapter XXIX) are also effective at those times for the Curculio, though later similar applications may also be necessary if the insects are abundant. (5) Where only a few stone-fruit trees are involved, jarring them early in the morning, after spreading white cloth under them, is a good treat- ment. The beetles at that time of day are sluggish and drop onto the cloth when the tree is given a sudden blow, and they can then be gathered and destroyed. This should be begun as soon as the blossoms have all fallen and continued until the beetles no longer appear. The Plum Gouger {Coccotorus scutellaris Lee). — This plum pest like the last, is a native of this country and is found from New York west to the Rocky Moun- tains and south to Texas. It appears to be destructive, however, mainly west of the Mississippi River. The adult (Fig. 134) is somewhat larger than the Plum Curculio. The head and thorax are dull yellow and the elytra are lead-gray in ' color, and the surface is without any humps or other irregularities. In many regards the habits of the Gouger are hke those of the Plum Curculio, but it leaves 140 APPLIED ENTOMOLOGY its winter quarters earlier than the last named insect and feeds for a time on the opening buds and leaves, gouging holes in tlie blossoms (Fig. 1346) and thus caus- ing them to drop off. Feeding holes and egg punctures in the young plums (Fig. 134c) are holes into the flesh in some of which the eggs are placed, but many- more holes are made than eggs deposited. The grubs work their way to and into the stone or pit and feed on the flesh (seed) within until full grown. Each then gnaws a hole through the stone, after which it pupates inside the stone, the adult appearing in late August and September. There appears to be but one insect in a fruit. a b c Fig. 1.34. — Plum Gouger (Coccotorus scutellaris l,ec.): a, adult beetle about three times natural size; b, plum blossoms attacked at their bases by the beetle; c, young plums punctured by the beetle. {Modified from Minn. Agr. Exp. Sta. Bull. 66.) Plums attacked by the Plum Gouger do not drop, but mature on the tree, but such plums are worthless for market because of the injured spots and because of the deformed fruit produced. Control. — Picking off the injured plums before the beetles emerge in the fall has been recommended as a method of control for this insect, and jarring in spring has also been advised, though the beetles do not drop as freely as in the case of the Plum Curcuho. It is possible that spraying with arsenate of lead as for the Curculio, making the first application as soon as the buds are open enough to provide any surface for the poison to adhere to, may prove of some value. The Cotton Boll Weevil {Anthonomus grandis Boh.), — This is at the present time the most serious insect pest of cotton which we have. Recent estimates place the destruction by the boll weevil at about 400,000 bales per year, which at average prices for the cotton not thus destroyed would be many millions of dollars. Diversification of crops has come into practice, however, where the cotton crop has suffered, so that in a number of the affected States the total value of all crops after the appear- ance of the weevil, has been greater than before. In some cases then, the loss to cotton has been more than made up by turning to other crops, but the reduction in the amount of cotton needed for use in the world is important. The cotton boll weevil is a native of tropical America, whence it spread northward through Mexico, and about 1892 entered Texas. Since that time it has extended its area of infestation, reaching the Atlantic THE COLEOPTERA 141 Coast in Georgia in 1916 and in time it will probably be present every where in the cotton belt, except perhaps in the more arid portions and in places where it can find little protection during cold weather. The adult boll weevil (Fig. 135) varies considerably in size but aver- ages about a quarter of an inch in length. When it first emerges from the pupa it is light brown, but it soon becomes gray or almost black. It winters as the adult, hiding under rubbish, in cracks in the ground, in Spanish moss growing on the trees, or in fact in any protected place, though those which winter in the cotton fields appear to be least protected and hence least liable to survive, while those in wooded areas winter more successfully. a be Fig. 135. — Cotton Boll Weevil {Anthonomus grandis Boh.); a, side view of adult beetle enlarged about six times; h, larva (grub); c, pupa; both much enlarged. (From Sanderson: Insects Injurious to Farm, Garden and Orchard.) In spring the beetles leave their winter quarters, the time generally varying from March to the last of June. "In the spring and throughout the fruiting season of cotton the eggs are deposited by the female weevils in cavities formed by eating into the fruit of the plant. An egg hatches under normal conditions in about three days, and the grub immediately begins to feed. In from 7 to 12 days the larva or grub passes into its pupa stage, corresponding to the cocoon of butterflies and moths. This stage lasts from 3 to 5 days. Then the adult issues, and in about 5 days begins the production of another generation. Climatic conditions cause considerable variation in the duration of the stages, but on an average it requires from 2 to 3 weeks for the weevil to develop from the egg to the adult. Males and females are produced in about equal numbers. The males feed upon the squares and bolls without moving until the food begins to deteriorate. The females refrain from depositing in squares visited by other females. This applies throughout most of the season, but late in the fall, when all the fruit has become infested, several eggs may be placed in a single square or boll. As many as 15 larvae have been found in a boll. The squares are greatly preferred as food and as places 142 APPLIED ENTOMOLOGY for depositing eggs. As long as a large supply of squares is present, the bolls are not damaged to any serious extent. The bolls, therefore, have a fair chance to develop as long as squares are being formed." (Marlatt, Farmers' Bulletin 848, U. S. D. A., 1917). TheSe insects are extremely prolific. It has been calculated that from a single pair of the beetles in spring there might be 12,755,100 progeny by the end of the season, but many factors prevent this from actually being the case. Infested squares soon drop off the plant and on the ground generally become so heated as to kill the larvae in them. Parasites and other enemies, particularly ants, attack the insect, and other minor factors are of some value. All of these combined, however, only prevent a bad condition from becoming worse, and control measures must be resorted to. Control. — There are several control measures which seem to give par- tially satisfactory results. One of these is to destroy all infested plants in the fall, particularly in the southern part of the area where the weevil is found. This kills great numbers of adults about ready to hibernate, many more still in early stages in the plants, leaves no food for those escaping, and prevents the production of the latest beetles, thus reducing the num- ber to hibernate. It also permits fall or winter plowing which is good farm practice in cotton growing. Generally this destruction of the plants should occur in October, even though a little cotton is lost in this way. The destruction of any hibernating weevils wherever possible is advan- tageous. Crop rotation is also desirable, as many of the weevils winter near the cotton fields and do not fly far in the spring. Any methods which will hasten crop production, such as fertilizers, the use of early maturing varieties and early planting, are desirable. Dusting the young plants with arsenate of lead or arsenate of lime blown directly onto them has frequently given good results. The use of all these methods together gives considerable relief from the attacks of this pest, and the problem how far to go in carrying them out is largely one of their cost as compared with the value of the cotton which will be saved by the treatments. Hand picking of the weevils and of infested squares has not generally proved successful. As the insect has thus far been known to feed only on cotton and the wild cotton of Arizona (where it probably does not yet occur), the danger of its increasing on other food plants does not at present seem to exist. The White Pine Weevil (Pissodes strohi Peck). — This native enemy of the pine occurs practically wherever the white pine is found, viz., from New Bruns- wick and Canada west to Minnesota, and south to North CaroUna. It also attacks our other native pines and the spruces somewhat. The adults (Fig. 136) pass the winter in protected places, possibly in the ground, and in spring gather on the terminal shoots (leaders) of the pines, generally on the trunk leader in preference to those of the branches. Here, near the tip, J THE COLEOPTERA 143 they feed on the bark and soon cut tiny holes in it, placing their eggs in the holes. The borers which hatch from these eggs tunnel downward through the leader (Fig. 137) and by August have finished feeding and pupate in the tunnels. After transformation to the beetle has been completed, these escape to the outside by making round holes through the stems they are in. Later they hibernate for the winter. The adult beetle is about a quarter of an inch long, reddish-brown or some- what darker, with a white spot on each elytron not far from its outer end, which when the elytra are at rest brings these spots not far from the end of the body. There are also several irregular areas on the eFytra somewhat lighter than the ground color. Control. — Spraying the leaders before the beetles gather on them in the spring, with arsenate of lead, using one pound more than the standard formula for the paste, is one method of control. Collecting the beetles after they have begun to gather on the leaders is also practiced, jarring them off into Fig. 136. Fig. 137. Fig. 136. — Adult White Pine Weevil {Pissodes strohi Peck), enlarged nearly three times. {After Felt: N. Y. State Mus. Mem. 8.) Fig. 137. — Work of White Pine Weevil in terminal twigs of pine. {After Felt: N. Y. State Miis. Mem. 8.) a net held beneath, as they generally drop instead of flying when disturbed then. This treatment should be repeated several times at 4 or 5-day intervals. It can hardly be done except on small trees. The injury caused by these insects aside from their feeding, is the kiUing of the leader which stunts the growth of the tree. Usually a side branch grows up to replace the lost leader and makes the tree deformed, or when two do this, a fork is produced. In either case the value of the tree either for timber or as an orna- ment is largely lost. The work of the weevil is most serious and also most frequent on young trees, making its injuries more serious on this account. The Alfalfa Weevil {Phytonomus postic^is Gyll.). — This European insect was discovered in this country about 1904 and is now found in parts of Utah, Idaho and Wyoming, and is gradually spreading. The adult (Fig. 138) is a snout beetle only about three-sixteenths of an inch long, brown when fresh but almost 144 APPLIED ENTOMOLOGY black after a time. It winters as the adult close to the ground or in crevices there, and in some cases under rubbish, and in severe winters many are killed by the cold. As soon as warm days come the weevils become active and lay eggs in the dry alfalfa stems, before the regular laying season, and the larva? from these eggs attack the young plants, often causing serious injury. The weevils also feed on the plants quite freely at this season. After a few weeks the true egg-laying period begins and the adults now puncture the living alfalfa stems and lay their eggs in them, this process usually being finished by the tenth of June, though a few eggs are laid much later. The eggs hatch in about ten days and the larva? (Fig. 139) consume the alfalfa leaves, those from the ones laid early beginning to Fig. 138. Fig. 139. Fig. 140. Fig. 138. — Adult Alfalfa Weevil {Phytonomus posticus GyU.) much enlarged. (From U. S. D. A. Bur. Ent. Bull. 112.) Fig. 139. — Side view of larva of Alfalfa Weevil, greatly enlarged. {From U. S. D. A. Bur. Ent. Bull. 112. Fig. 140. — Cocoon of the Alfalfa Weevil, greatly enlarged. {From U. S. D. A. Bur. Ent. Bull. 112.) feed in May, while later individuals are feeding until into July or even August, with some stragglers later. The larval period varies greatly, but an average length of time in this stage would be perhaps a month. When full-grown the larva goes to some protected place such as a dry, curled leaf or dead vegetation near the ground and spins a cocoon (Fig. 140) in the form of a loose network, in which it pupates. This stage lasts about 10 days before the appearance of the beetle. In late summer these beetles begin to look for winter shelter and in this search may spread some distance. In spring a somewhat similar flight in search of food, also increases their spread. This insect feeds on various species of clover in addition to alfalfa, and as it seems to be persistently spreading, it must be considered a menace to nearly all parts of the country. Control. — The most serious injury to the crop is that caused by the spring feeding before the first cutting, and this also delays the production of the second crop. Any treatment of the field, such as disking it with a harrow, which will hasten growth at that time will be a gain. Spraying these fields with arsenate of lead, 1 lb. of the paste in 50 gal. of water, appears to reach many of the insects and be quite effective. Pasturing during the spring months, dividing the fields so that each piece may be grazed close about once every 2 weeks, and continuing this until most of the eggs of the weevil have been laid, has also given good results, as has cutting and feeding the crop before the eggs hatch. Spraying THE COLEOPTERA 145 the stubble after the first cutting, or treating such fields by going over them once or twice with a disk or spring-tooth harrow, followed by dragging with a brush drag, to give a dust mulch, will protect the second crop but is i^robably less valu- able than the earlier spring methods. The Potato Stalk Weevil {Trichobaris trinotata Say). — This pest of the potato is widely distributed over the United States east of the Rocky Mountains except in the more northerly States. It has also been reported from California. The beetle is gray with a black head and three black spots at the base of the elytra and is about a fifth of an inch long. It winters in the old potato stalks and when the young potato plants are large enough it makes small holes in the stalks and sometimes in the branches, in which the eggs are deposited; The eggs hatch in a week or 10 days and the grubs burrow downward toward the roots and after reaching them turn upward again, enlarging the burrows. This tunnelling weakens the stalks and causes the plant to wilt and die. Pupation takes place in the stalks, usually near the ground, and the adults are produced in from 1 to 2 weeks, but generally do not leave the stalks until the following spring. A number of individuals may be present in a single stalk. Other food plants are Jamestown weed, horse nettle, eggplant and other plants of the family Solanacea?. Control. — Where the plants have wilted and dying leaves, and an examination of the stem shows borers to be present, pulling up and burning infested stalks is desirable. Prac- tically the same result may be obtained by collecting and burning^ all the stalks as soon as the crop has been dug, thus destroying the weevils in them. The . destruction of all weeds around, which are liable to be infested by the insects, this work being done after the egg-laying season is over, is also desirable. The Sweet Potato Weevil (Cylas formicarhis Fab.). — This is a tropical insect which was first reported in the United States about 1875. It now occurs in the most southerly States from Georgia to Texas, attacking the sweet potato. The adult (Fig. 141) unlike the other snout beetles here considered, is very slender, about a quarter of an inch long, with a black head, reddish prothorax and legs, and dark blue elytra. The prothorax is strongly narrowed, forming a noticeable "waist" for the insect. The eggs of this pest are laid singly in small holes eaten in the stem or any exposed potato. They hatch in a few days and the grubs in the stems burrow through them down to the potato, then tunnel irregularly about, becoming full- grown in 2 or 3 weeks. The grub iiow forms a cavity and in this it pupates for about a week and then a few days later eats its way out and may leave the potato, or may remain there and lay eggs for another generation in the same potato in which it itself developed, and this process may continue until the entire potato is destroyed. As long as food is available, one generation after another is thus produced, but when no more can be found the adult insects live along for a considerable time without feeding, attacking the plants and laying their eggs in them whenever more appear. Adult beetles feed on the leaves and stems somewhat. 10 Fig. 141.— Adult Sweet Potato Weevil {Cylas formicarius Fab.) enlarged over five times. {From U. S. D. A. Farm. Bull. 856.) 146 APPLIED ENTOMOLOGY As soon as tunnels in the potato are formed, the tissues around them change color and decay soon follows, so that an attack quickly ruins the value of the crop. Control. — Sweet potatoes found infested ever so slightly should immediately be destroyed, either by feeding to stock or in some other way. If any area becomes infested no sweet potatoes should be planted there for several years, and as it is probable that the insect can also breed in the wild morning glory, all plants of this species should also be destroyed as far as possible within the area. Spraying the plants with arsenate of lead or other stomach poison, applied as soon as the beetles appear has recently given encouraging results. Following sprays at about ten-day intervals may be given if necessary. Family Ipidae (formerly Scolytidse) (Bark beetles or Engraver beetles). The members of this family are borers and nearly all attack the inner bark or wood of trees. They are small insects, from one twenty-fifth to two-fifths of an inch long, brownish or blackish in color, and usually with cylindrical bodies (Fig. 142). In habits they form two chief groups. In the so-called Ambrosia-beetles the tunnels extend through the wood and the young develop there: in the True Bark-beetles the tunnels are formed either in the inner bark or between this and the wood. The adult in Fig. 142. i'lG- 143. Fig. 142. — Adult Bark Beetles, greatly enlarged. {Modified From Felt: ISf. Y. State Mus. Mem. 8.) Fig. 143. — Work of Bark Beetles on inside of bark, slightly reduced. {Original.) either case cuts a tunnel slightly larger than itself in to the inner bark or through this, but the Ambrosia-beetles continue it on, into the wood. The Bark-beetles having arrived at the desired depth, turn and excavate one or more channels between the bark and the wood, which become the egg tunnels. Along the sides of these the eggs are deposited, either singly in little hollows, several together in larger excavations, or THE COLEOPTERA 147 many in grooves of tho tunnel. The larvse, on hatching, excavate tun- nels for themselves, leading away from the egg tunnel (Fig. 143) and becoming larger with the growth of the larvae. Pupation is at the end of the larval tunnel in a somewhat wider portion and after transforma- tion the adult bores its way to the outside. In the case of the Ambrosia- beetles a fungus used as food by the insects, grows on the walls of the tunnels and generally turns these walls black. Destruction by these insects is mainly of forest and shade trees. As nearly all the bark-beetles appear to prefer dying bark in which to live, the refuse of cutting operations, commonly termed "slash," will provide much of this, and most of the insects will work there. When slash comes to an end, however, by operations ceasing in that area, the increased abundance of the insects due to abundant slash often forces them for lack of other material, to turn to the healthy trees, themselves changing thereby from "secondary" to "primary" foes. Slash should therefore be destroyed before beetles in it can develop to the adult condition. Fire in forests produces many dead and weakened trees also, frequently lead- ing to insect attacks, and epidemics, either local or quite widespread, may thus result. Many trees when the beetles bore into them, pour out their sap or resin, and some of the insects may easily be drowned in this. If attacked by multitudes, however, the supply of sap becomes so reduced that the insects coming later can accomplish their purpose. Removing "beetle trees" before the adults escape, and either remov- ing and burning the bark, floating the logs, or sawing the same winter and burning the slabs and trimmings, are some of the measures used for the protection of our forests against these insects. One species of Ipid, the Clover Root-borer, tunnels in the main roots of clover. Several other species attack fruit trees, usually those not healthy. The Fruit-tree Bark-beetle or Shot-hole Borer (Eccoptogaster rugu- losiis Ratz.). — This European fruit-tree pest has now been in the United States about 50 years and is present nearly everywhere east of and in many localities west of the Mississippi River, and has been reported from California. It breeds in most of the cultivated deciduous fruit trees as well as in several kinds of wild ones. The beetle (Fig. 144) is about a tenth of an inch long, almost black, except the tips of the elytra and the legs, which are dull red. In the spring the beetles enter the trees and dig out egg channels one or two inches long, about parallel to the grain of the wood, partly in this, partly in the inner bark. Here, in little niches or hollows along the sides, the eggs are laid. These hatch in a few days and the grubs burrow, first directly away from the egg channel, then turning in various directions, extend these larval tunnel sseveral inches, and pupate at their ends. 148 APPLIED ENTOMOLOGY When the beetles have been formed there, they bore out to the surface of the tree (Fig. 145) and soon begin to tunnel in again, to lay eggs for a second generation which in the North becomes adult before winter, thus giving two generations a year. In the South with its longer warm Fig. 144. — Fruit-tree Bark-Beetle {Eccoptogaster rugulosus Ratz.) ; a, Adult Beetle; h, side view of same; c, pupa; d, larva. Hair lines show true length. {From U. S. D. A. Farm. Bull. 763.) season, three or perhaps four generations may be produced each year, the adult beetle in some cases at least, wintering in the tree, while in others this season may be passed in the egg stage. Healthy trees are not often attacked except when the beetles become so abundant that a sufficient supply of weak or dying ones is not available. Fig. 145.- -Exit holes of the Fruit-tree Bark-Beetle in bark of a young tree, about natural size. (From U. S. D. A. Farm. Bull. 763.) In healthy trees the flow of gum sometimes prevents the development of larvcB but in time this becomes less and the insects then have a weakened tree to attack. Trunk, branches and twigs are perhaps equally liable to be injured. The burrows extending in all directions, partly in the outer THE COLEOPTERA 149 surface of the wood, partly in the inner bark, destroy the cambium or growing layer, often entirely girdling the twig, branch or trunk as the case may be, and causing its death. Control. — This must largely be accomplished by measures to keep the trees as vigorous and healthy as possible. Any injured, broken or otherwise affected limbs should be removed or so treated if possible, as to restore them, and close watch of trees outside the orchard, liable to infestation, should also be given. Infested trees which are still pouring out gum can sometimes be saved by cutting back strongly and then culti- vating and fertilizing freely. In some cases a thick coat of whitewash mixed with a little table salt can be applied as a repellent for the beetles. This treatment sometimes needs to be applied three times — once in spring, again in midsummer, and once again in the fall. Washes of soap and carbolic acid have occasionally been used with some success, and it is claimed that the larvse can be killed in their burrows by using a carbo- lineum spray material. This is made by dissolving 3 lb. of naphtha soap in 3 gal. of hot water; adding a gallon of carbolineum, stirring thoroughly and then diluting for use at the rate of 1 part of this to 4 of water. These methods should work equally well for any of the barkbettles where the bark is no thicker than at the places where these insects attack the fruit trees. CHAPTER XX THE STREPSIPTERA These tiny insects are seldom seen except by entomologists, and their parasitic habits aid in their concealment. For a long time opinions were divided as to where they belonged, some regarding them as a family of aberrant Coleoptera, while others considered them as forming an order. Recent studies seem to confirm the latter view and the group is now generally rated as a separate order, though its closest relations are probably with the beetles. The Strepsiptera, from the meaning of this name, may be called the Twisted-wing Parasites, though the words stylops and stylopid are fre- quently used in referring to them. The males on reaching the adult condition (Fig. 146), become free and can fly. The females on the other Fig. 146.- -Male Strepsipteron (Xenos vesparum Rossi), rather more than six times natural size. {After Pierce.) hand, remain partly within the bodies of their host insects and are worm- like or grub-like (Fig. 147) in appearance. The males are very small, soft-bodied animals, ranging from about one to perhaps four twenty- fifths of an inch in length. The eyes are more or less stalked and the antennae have one or more segments elongated on one side. The mouth parts are greatly modified but appear to be of the chewing type, though the adult does not feed. On the mesothorax is a pair of tiny clubs, some- times rather flattened, which represent the front pair of wings. The metathorax forms nearly half the entire length of the body. It bears a pair of well developed wings which are broad and fold lengthwise when at rest. The abdomen is composed of ten segments. The females are soft and resemble a rather long sack bearing traces of segmentation, and at one end a constriction, beyond which is a sort of knob, believed to be a 150 THE STREPSIPTERA 151 combination of the head and thorax; a cephalothorax in fact. This portion of the body is pushed out between two of the body segments of the host (hiring the latter part of the metamorphosis, thus becoming external (Fig. 147) and the body of the host is distorted in this way. The members of this order may be characterized as follows: Tiny insects which from the first larval instar to the adult, are internal parasites in other insects. The male adult has stalked eyes, mouth parts of the chewing type, but little or not at all developed; antennce with one or more segments prolonged laterally; pro- and mesothorax small, the latter with a pair of small clubs corresponding to the fore wings of most insects; meta- thorax long, forming at least half the length of the body and bearing a pair of Fig. 147.— Female Strepsipterou, top and side views and a Stylopized Wasp: a, end of the parasite projecting between the abdominal segments of the AVasp. All greatly enlarged. (After LeuckarV s Wandtafcln.) broad wings which fold longitudinally. The female adult is worm-like, without feet, and located within the body of its host except for a cephalothorax which protrudes between two abdominal plates of the latter. It is enclosed by its pupa skin. Metamorphosis complete. These insects, often called "stylops," are parasitic only in some Orthoptera, Homoptera, Hemiptera and Hymenoptera, as far as known, and at the present time only Gryllotalpa in the Orthoptera and Chryso- coris in the Hemiptera are known as hosts in those groups. Most of the parasitism is of leaf-hoppers, wasps and the solitary bees, and these are so disabled by the removal of their body fluids by the parasites that "stylopized" individuals are unable to reproduce and are greatly lacking in vitality. Their bodies are often distorted also and other changes are produced. 152 APPLIED ENTOMOLOGY The eggs of the stylops appear to hatch within the body of the mother and the young escape by passing from the body out into the space between this and the pupa case of the parent in which it remains, and then through an opening in this at the cephalothorax, thus reaching the open air. They are now on the body of the parental host and this insect may carry them to its nest, where if it is a colonial form, the stylops may find young to attack there. It is generally probable though, that they leave the parental host at some place (possibly a blossom) where other insects of the host species will be liable to visit. Transferring onto such individuals as chance may permit, the stylopids finally arrive where larvae of the proper species are available, and at once attack them. Thus far they have been active little six-legged larvse, but after burrowing into the body of their host larvse they change greatly, becoming worm-like and legless. The males finally enter a pupa stage, after which the adults escape, but the females remain throughout the rest of their life in the bodies of their hosts. Where stylopids are abundant and attack injurious species of insects, such as are most at least of the Homoptera, the stylopized individuals, being unable to reproduce, become of lessened importance and their parasites must be considered as beneficial. Most of the Hymenoptera they attack, however, are beneficial and parasitism in such cases can hardly be considered helpful to man. The group is not sufficiently abundant though, to be an important factor under ordinary conditions, as only about a hundred species are known, but these are widely dis- tributed over the globe. CHAPTER XXI THE THYSANOPTERA The Thysanoptera — sometimes called Physapoda — are very small insects, peculiar in many ways. The common name for members of this group is Thrips, unchanged in spelHng whether one or many are referred to. As a whole these insects appear to have some affinities with the hemip- teroid groups (Anoplura, Hemiptera and Homoptera) yet to be consid- ered, but are generally looked upon as forming an order by themselves, though in some regards they seem to have certain relations to the Cor- rodentia and Mallophaga. It is not improbable that they form a group originating not far from the common trunk of all the above-named orders. Thrips vary from one-fiftieth to one-third of an inch or more in length. Their mouth parts (Fig. 148) form in part a short, stout cone attd,ched far back on the underside of the head, composed of the labrum, a portion of the maxillae, and the labium. Within this cone are three bristles consisting of the lobes of the maxillae and one mandible, the other not being developed. The animals are sucking insects. Four wings p^^ i48.— Side view of are usually present, rather long and narrow, with the head and prothorax of , p . 1 1 1 • 1 1 11 • a Thrips to show the mouth few vems, and frmged behmd and generally m ^^^^^ ^p^^^ ^ s. D. A. front also, with slender hairs, longer than the Bur. Ent. Bull. 68 Part 2.) breadth of the wing itself. When at rest the wings lie flat on the top of the abdomen. In some cases they are greatly reduced in size or may even be wanting entirely. The tarsi are com- posed either of one or two segments, usually the latter: at the tip is a bladder-like portion which can be drawn into the segment or pushed out. The abdomen consists of ten segments, the last either conical or tubular in form. Summarizing these facts, the adult Thysanoptera may be described as: Small insects with greatly modified mouth parts forming a cone attached to the hack part of the head beneath and used for sucking. Wings four, generally present, long, narrow, with few veins, and fringed behind {usually in front also) with long hairs. Tarsi of one or two segments, the tip with a bladder-like swelling capable of being drawn into the tarsus. Abdomen of ten segments, the last either conical or tubular. Metamorphosis incomplete but approaching completeness. 153 154 APPLIED ENTOMOLOGY Thrips feed on plant juices, puncturing the tissues and extracting the sap, leaving white marks or streaks where the cells without their juices have dried. They attack stems, leaves and blossoms, in the last case often blighting them and preventing the setting of fruit. On leaves of plants the under surface appears in most cases to be the preferred place of attack and the insects do not move about much. With grasses and cereals the stems as well as the leaves suffer, thus checking the growth of the top, and in some cases the kernels of growing grain are also fed upon. Some species live under loose bark and a few have been reported as feeding upon other insects. In many cases the injury caused by these insects is very serious. In one section (Suborder Terebrantia) the female has an ovipositor with which she saws slits in the epidermis of plants, placing an egg in each slit. In the other section (Suborder Tubulifera) there is no ovi- positor and the eggs are laid upon the surface of the food material. The larvae considerably resemble the adult. After from two to four molts they leave their food to find some more protected place and there molt again, at which time wing stubs appear and other changes can be seen. Another molt and now the insect becomes quiet unless disturbed, not feeding, and marked changes become evident, bringing it more nearly like the adult, and the completion of these changes is followed by a molt which produces the adult itself. This is more than a typical incomplete metamorphosis, yet not entirely comparable with a complete one. It may be regarded therefore as intermediate between the two. In some cases parthenogenesis, i.e., the production of the next gener- ation by unfertilized females, occurs. This is perhaps to some extent determined by weather conditions, in this group. Parthenogenesis is frequently present here and there among insects and will be considered more fully elsewhere. Driving rains are very destructive to all kinds of Thrips. Lady beetles and other insects of several species feed freely upon them. The Wheat or Strawberry Thrips (Frankliniella tritici Fitch). — This is probably the most widely distributed species of the group in this country. It feeds on wheat, strawberry, apple and many other plants and where the blossom is attacked as in the case of the strawberry, it is blighted, preventing the formation of the fruit and producing the stunted struc- tures known as "buttons," instead. Leaves attacked often curl and be- come malformed, the particular parts injured soon turning brown and dying. In California it is a particular pest of alfalfa. The adult is about a twentieth of an inch long, yellowish in color. In the warmer parts of the South it is more or less active at all seasons of the year, but in the North it winters in protected places, many probably, like other species, in grass fields close to the ground. The life history in the South requires about 12 days but is probably THE TIIYSANOPTERA 155 longer in the cooler temperatures of the northern states, and several genera- tions are produced in a season. Control. — In general, spraying with nicotine sulfate 40 per cent, standard formula, or with kerosene emulsion, 1 part in 4 parts of water, is a good treatment. Success with these materials, however, depends largely upon the thoroughness of the application and the number which are killed. A favorite formula in California consists of 13^^ gal. of com- mercial lime-sulfur, and 33^^ fl. oz. of nicotine sulfate 40 per cent in 50 gal. of water, applied as a spray. Where the adults are wintering in grass fields and it is practicable, burning these over will destroy many. The Onion Thrips {Thrips laoact Linde.;. — This pest is present practically everywhere in Europe and the United States, having first been noticed here about 1872 (Fig. 149). The adult is about a twenty-fifth of an inch long, rather light yellow, but turning brown as it becomes older. It feeds on a great variety of plants but being the species which is particularly injurious to growing onions, is generally known as the Onion Thrips. The onion leaves are whitened by the removal of their juices, and soon begin to bend sharply downward, and later they may curl or twist and even die, an area much affected in a field being noticeably pale colored and the plants stunted, while the bulbs make little growth. Winter in the North is spent as the adult in protected situations such as in dead grass close to the ground or in rubbish left on the field. In spring the young onion plants are attacked soon after they come up, first in the bud, later on the leaves, in which the eggs are laid. The life cycle from egg to adult is influenced by the tempera- ture, varying from a little less than 3 weeks to over a month, and in the most southerly states the generations overlap so that practically all stages may be found at the same time. Sometimes in the North this insect becomes a greenhouse pest on roses, carnations, cucumbers and tomatoes, though the Green-house Thrips {Heliothrips hcemorrhoidalis Bouche) is most often responsible for this injury. Control. — Any methods of farming which will reduce the oppor- tunities for this insect to pass the winter successfully, are of value. The destruction of all refuse on the field after the crop has been gathered: fall plowing of such fields, and burning over grass lands adjacent to them, at the proper time in the spring, are all beneficial. Cultivation and fertili- zation to push the crop ahead early to "keep it ahead of the thrips" is Fig. 140.— Xyniph of the Onion Thrips (Thrips tabaci Linde.), greatly enlarged. {From Britton : Third Rept. Conn. State Entomologist.) 156 APPLIED ENTOMOLOGY also helpful. Spraying the plants with nicotine sulfate 40 per cent, % pint., 4 lb. more or less of soap, and 50 gal. of water is a fairly effective treatment. Fish-oil soap is better than laundry soap when obtainable, and the amount to use is determined by spraying a leaf with the mixture. If the spray gathers together into larger drops, leaving parts of the leaves dry, more soap is needed, for its use is mainly as a "spreader" over the leaf surface. This treatment should be repeated every 8 or 10 days as long as the Thrips are present in any abundance, until within a month of harvesting. Use a fine, misty spray with con- derable pump pressure. Only thorough spraying will give effective results. The Pear Thrips (Tceniothrips inconsequens Uzel). — This insect was first discovered in the United States in the central part of California, /'""'^|% Fig. 150. — Adult Pear Thrips {Tceniothrips inconsequens Uzel), greatly enlarged. (.From U. S. D. A. Bull. 173.) attacking deciduous fruit trees, particularly pears, prunes and cherries, blighting the blossoms by the abstraction of their sap. Later it was found in British Columbia, in the Hudson River Valley in New York, and still later in Pennsylvania, Maryland, and in England. Recently it has been learned that the insect was first discovered in Bohemia, feeding in blossoms. The destruction caused by this pest in California has been very great some years. The crop of prunes in the Santa Clara Valley alone has been estimated as having been reduced in the 7 years, 1905 to 1911, 141,000,000 lb. The injury is caused by the feeding of the young and adults on leaves, buds, flowers and fruit, -and by laying eggs in the leaves and fruit stems and also in the small fruit. THE THYSANOPTERA 157 The dark brown — almost black — adults (Fig. 150) appear early in spring, coming out of the ground about the time the fruit buds are swelling and opening, and as soon as these have opened slightly the insects work their way into them and feed on the most delicate parts. The eggs are laid mainly in the young leaf and fruit stems and young fruit and hatch on an average after about 8 days. The nymphs (Fig. 151) feed on the leaves and young fruit forming a sort of ''scab" on the surface of the latter, and remain on the tree for 2 or 3 weeks, though from the first young to appear to the last young to disappear, may be more than 2 months. When through feeding they fall to the ground, which they enter for a varying distance, and there, after from 2 to 5 or 6 months, they transform to the last stage before the adult, having previously molted once under- ground. Late in the fall or winter the final molt produces the adults which remain in the ground till early spring. This remarkable life history, quite unlike anything known for any other Thysanoptera, permits but one generation a year, with active injury during only a rather short period in the spring. Control. — These insects can be destroyed by spraying with Nicotine sulfate 40 per cent used at the rate of 1 part to 800 parts of water, stand- ard formula. Success with this treatment, how- ever, is entirely dependent upon the thoroughness of the application. The first treatment should at once follow the discovery of the Thrips upon the swelling buds and should be repeated at least every 2 or 3 days until the buds are open or the Thrips have become very few. No spraying should be done from the time the blossoms open until the petals fall. Then, if Thrips are abundant on the remains of the blossoms, another treatment should be given. The Citrus Thrips (Scirtothrips citri Moult.) is a rather serious pest in California and Arizona. It feeds upon the tender stems, leaves and fruit of citrus trees, and occasionally also attacks the grape, apricot and other plants. With seedling plants the leaves and buds are injured and growth is checked. The fruit is injured by scars and scabs caused by the feeding, and greatly reduced in value, and some drops to the ground. The adult is one of the smallest of the Thysanoptera, varying from one-fiftieth to one-twentieth of an inch in length, and is orange-yellow in color. The young appear in April and May and gather on the leaves i^ Fig. 151. — Nymph of Pear Thrips, greatly en- larged. {From U. S. D A. Bur. Ent. Bull. 68, Part 1.) 158 APPLIED ENTOMOLOGY and fruit where they remain until the midsummer hardening of these parts leads most of them to leave for various other food plants, until August and September when they return to the citrus trees again and lay their eggs in the leaves and stems of the plant. These winter over and hatch the following spring. Following the production of adults from the hatching and development of these eggs, there may be six to eight generations during the season and all stages may be present at once on a tree as late as December, though these die with colder weather, leaving only the eggs to hatch in the spring. The last stage before the adult, during which the insect is quiet, is passed in crevices of the trunks or in rubbish under the trees, but not in the ground. Control. — Spraying, either with lime-sulfur wash using 1 part (if of a density of 33°B4.) in 50 parts of water, or with more water than this if the wash reads higher; or with Nicotine sulfate 40 per cent, at the rate of 1 part in 800 parts of water, have given excellent results. The first application should be made as soon as four-fifths or more of the blossoms have fallen, and a second 10 days to 2 weeks later. If these two treat- ments have been well-timed and thorough, the third can be delayed until about 3 weeks after the second. A fourth treatment late in August or early in September, if the returning insects are very abundant on new shoots, will aid much in checking their increase. In all treatments the application should be very thorough and with a pressure of at least 1251b. Particular attention should be given at the second application to completely drenching the fruit and any tender leaves. In addition to the species of Thrips given separate consideration above, nu nerous other species are frequently of some importance. Among these the Grass Thrips which sucks the sap from the stems of the lighter grasses, turning them white and killing them, thus causing "silver top" as it is called; the Greenhouse Thrips which attacks tomatoes, cucumbers and many other plants in greenhouses in the North and out- of-doors in the South, and the Camphor Thrips which is a serious pest of the Camphor tree in Florida, are perhaps the most important. CHAPTER XXII THE CORRODENTIA Most of the Corrodent ia are very small, even tiny insects, though a few giants of the group found in South America have a wing-spread of about an inch. Some of the group are wingless and are most often noticed as small, whitish, gray or brown specks running over the leaves of old books. These are generally called Book-lice. The winged forms (frequently called Psocid^, though this name really applies to the entire group) when adult are somewhat larger and are found on tree trunks, weathered fences and other places where lichens grow, and furnish them with their food. In general the members of the group eat animal or vegetable refuse, mould, fungi and similar materials. Several hundred kinds are known. The body in the Corrodentia though quite soft, is well developed, but the pro- thorax is small and concealed in some cases between the head and the mesothorax. In others it is distinct, but as the meso- and metathorax are grown together in those cases, only two of the three thoracic seg- ments are evident. The antennae are rather long and slender, and the mouth parts are for chewing but considerably different in some details from the typical structure. The wings when present are four in number, with very noticeable veins, few of which are cross-veins. When at rest the hinder margins of the wings of the opposite sides are brought together over the back of the insect with their upper surfaces sloping down at the sides, thus assuming the position of a steep house roof. They are often more or less dusky or mottled. The tarsi consist of only two or three segments. Ocelli may be present in the adults but not in the nymphs. These are quite similar to the adults otherwise, and develop through a series of molts into the adult condition. The group may be characterized as follows : Small, soft-bodied insects with or without wings when adult. In those having wings there are two pairs, with prominent veins: when at rest they 159 Fig. 152. — Adult Booklouse about fifty times natural size. (From U. S. D. A. Farm. Bull. 1104.) 160 APPLIED EJ^TOMOLOGY are held at a sharp angle over the body, hinder margins uppermost. An- tennce long and slender. Tarsi of two or three segments. Ocelli sometimes present in the adult condition. Metamorphosis incomplete. This little order contains few species of much economic importance. The wingless forms — book-lice (Fig. 152) — found in buildings, eat the paste and paper of old books and are also found in birds' nests where they find in feathers and other organic debris their food. The winged forms, frequently called Psocids, are found in various places, but perhaps most frequently on the trunks of trees, generally in clusters and often in various stages of their development. They have the power of producing silk and sometimes the clusters appear to be covered, at least partly, by a web of this. Fig. 153. — Adult Psocids: a, side view showing position of wings at rest; 6, Psocid (Psocus lineatus) with wings spread. Both greatly enlarged. {From Sanderson and Jackson, Elementary Entmology: a, after Kellogg: b, after J. B. Smith.) Some of the book-lice are claimed to be able to make a ticking sound something like that of a watch, and this sound is often called the "death watch," Such a sound is certainly produced by a small beetle, and the possibility of the book-lice also being able to make it has been questioned. The weight of evidence thus far, however, seems to favor this possibility. It is heard chiefly in old houses at night or when everything is quiet, as a faint, rapidly repeated tick-tick-tick, and is in all probability, the call of an insect to its mate. The winged Corrodentia (Psocids, Fig. 153) are not known to be of any economic importance. Where the wingless forms (book-lice) be- come extremely abundant in buildings, relief may be obtained by a thorough cleaning of the infested places. Light and air, particularly dry air, are unfavorable to them, and heating a room to quite a high temperature for a few hours and the exposure of all the furniture to sunlight for a time on a bright day will generally free the place from these insects. All stages except the egg appear to die at the beginning of winter. CHAPTER XXIII THE MALLOPHAGA The Mallophaga are generally called bird-lice but as they feed by biting off particles of feathers, hairs and scales of the skin, from the animals on which they live, the name biting-lice would be better as it would dis- tinguish them more accurately from a large number of very similar insects found in many cases on the same animals, which feed by sucking the blood of their hosts, and which are called sucking-lice. 4J^ Fig. 156. — Samples of Anoplura or Sucking Lice, greatly enlarged. {After Dalla Torre.) Anoplura (Fig. 156) occur on man, monkeys, domestic animals, rats, mice, rabbits, squirrels, the elephant, etc., and one genus is found on the seal. The mouth consists of a flexible proboscis which may be drawn in or pushed out, turning inside out as it goes and exposing some chiti- nous hooks which attach themselves to the skin of the host. Lodged in the head are two long, slender, sharp-pointed structures called stabbers, one, possibly both, apparently double in nature but more or less fused, and so placed as to form a canal between them through which saliva may 164 THE ANOPLURA 165 be injected into the wound they make. These stabbers are forced through the skin within the area encircled by the proboscis, saHva is forced into the wound and after a few moments feeding begins, the blood of the host being pumped into the body of the louse. Eggs or "nits" are laid singly, attached to the hairs of the host or in some species, to the fibres of the clothing. They hatch in from 1 to 2 weeks, according to the species and the temperature, but when the latter remains low, as where the eggs do not feel the effects of the warmth of the host, they will not hatch (at least with the lice infesting man). The nymph stage probably requires 8 to 10 days, though practically nothing is known of the development except with the lice attacking man. Several hundred eggs are usually laid by each female during a period of nearly a month, so that a heavy infestation becomes possible in quite a brief time. The Anoplura is a small group of insects, probably only about a hundred species being known. They were formerly considered degener- ate Hemiptera, but with the division of the old Order Hemiptera into separate orders — the Hemiptera in a more restricted sense and the Homoptera — it has seemed more logical to regard the Anoplura as also an Order, most closely re- lated to these, but still sufficiently different to entitle it to ordinal rank. The Human Body Louse {Pediculus humanus L.).^This pest (Fig. 157), which during the European war also received the common name "cootie," is now generally regarded as being of two races, the head louse (formerly called Pedi- culus capitis) which is found chiefly on the head, and the body louse {formerly Pediculus vestimenti or P. corporis) found mainly on the clothing, rather than different species, but the races differ somewhat because of different conditions under which they live. This insect under ordinary conditions of cleanliness can be easily controlled, but in camp hfe finds an opportunity to increase, often almost without possibility of being checked. Under ordinary conditions a simple treatment for the race living on the head is to wash thoroughly with tincture of larkspur, which can be obtained of a druggist, and repeat this two or three times at intervals of about a week. For the race living on the body, treatment is somewhat different, as the pests are largely on the clothing, reaching across from this to the skin to feed. Here boiling all clothing which can be so treated, dry heating the rest to 130°F. for 3^^ hr. and taking a hot bath will usu- ally be sufficient. Fig. 157. — Human Body Louse (Pediculus humanus L.) about eight times natural size. (From Beilese.) 166 APPLIED ENTOMOLOGY Rather recently it has been discovered that the hce of man are con- cerned in the transmission of Relapsing fever, Trench fever, and that terrible disease Typhus fever. It does not at present seem that the causal agents of the first two of these are actually transferred to man by the feeding of the infested lice, but rather that these agents are present in their bodies and feces, and that by scratching parts irritated, fluids from crushed lice or the feces get rubbed into the irritated areas, are able to enter the body, reach the blood and begin the disease. This also appears to be true in the case of Typhus fever, but here inoculation by the feeding of the lice also seems probable. In some cases where scratching does not occur but where Relapsing or Trench fever nevertheless develops, it is probable that the feces get into the feeding wounds and in that way cause the disease. The Crab Louse {Phthirus pubis L.). — This louse is quite different in appearance from the last, being smaller, shorter, broader, and with its legs projecting outwardly near together (Fig. 158). The fore legs are slender but the others are stout and each has a powerful serrated claw which shuts against a pro- jection of the preceding segment of the leg in such a way as to give a very firm grip on a hair. This insect is found primarily on the hairy parts of the body except the head, but in exceptional cases it may be found there also. It holds onto the hairs while feeding and in moving about always holds tightly to hairs on one side until it has obtained a grasp on others on the other side. This gives it a sideways move- ment which is responsible for its common name. Its life history is much the same as in the other species. Washing thoroughly with tincture of larkspur as for the head louse is usually an effective treatment. An ointment made of 4 parts of crude naphthaline mixed with 1 part of soft soap rubbed on the undercloth- ing in the infested region has also been found to be a very successful treatment. Lice on Domestic Animals. — These are sometimes serious in their attacks, weakening the animal greatly if they are abundant. In the treatment of these pests it should be borne in mind that poisonous materials cannot be used because of the danger coming from the animals' licking themselves. Various substances have been used for hve stock, such as 15 per cent kerosene emulsion scrubbed on the skin; washing with potassium sulfid, using from 2 to 4 oz. per gallon of water according to the size and vigor of the animal; the application of a mixture of sulfur Fig. 158. — Human Crab Louse (Phthirus pubis L.) about twelve times natural size. (From Berlese.) THE ANOPLURA 167 1 part, lard 4 parts, rubbed over the body, or washing with dikite car- bolic acid using 1 part of the acid in 30 parts of water. The most usual treatment for cattle lice, however, is by the use of stavesacre (Delphin- ium) seeds. Four ounces of these seeds and 1 oz. of white hellebore are boiled in a gallon of water until only 2 qt. remain. This is then applied with a brush to the animals. It may need to be repeated if more lice appear, showing that eggs or some of the lice escaped the first application. Raw linseed oil, applied with a brush has recently been recommended as an alternative treatment, the material for one animal costing about five cents. The relation of insects to disease as has been brought out above, where lice serve to convey the germs or parasites causing illness to man, is one of the newer subjects in Entomology but one which has been shown to be of great importance. Medical Entomology is already a large field upon which much has been written, and yet one about which little is probably known in comparison with its actual size. CHAPTER XXV THE HEMIPTERA The Hemiptera is a large group containing many insects which are always injuriously active, and many more which occasionally become so. They vary greatly in size, some being minute while others may attain a length of four or five inches. They are most numerous in species in tho warmer portions of the globe, but an abundance of individuals in colder regions results in making them extremely common everywhere. Most Hemiptera have the dorsal surface of the body rather flattened, though there are many exceptions to this statement, and the wings when not in use rest upon this surface. The wings are nearly always present, four in number, and the basal half, or sometimes more, of the front pair is thickened and horny, resembling the elytra of beetles. The outer end, however, is membranous and veins traverse this portion, so that the fore wings are appropriately called hemielytra. The membranous part of one wing largely overlaps that of the other when they are at rest. In a few families the difference in the texture of the two portions is not very perceptible but in most cases it is plainly evident. The hinder wings are entirely membranous and when not in use are concealed beneath the others. The body of the Hemipteron with few exceptions, shows no constric- tion at the junction of thorax and abdomen and is usually widest at the hinder end of the prothorax. The attachments of the wings behind this do not occupy anywhere near all of the width of the body, and directly behind the pronotum, between the wings, the space is taken up by a rather large, usually quite triangular plate called the scutellum. In some families this becomes greatly enlarged, covering more or less of the dorsal surface of the body from the pronotum back, and in such cases the wings in closing slip under this so that little besides their costas show. Hemiptera are sucking insects (Fig. 159), obtaining their food by piercing the surfaces of plants or animals and drawing into their own bodies the sap or blood. The mouth parts in the group have been identi- fied with those of chewing insects, but they have been greatly modified to form a beak or rostrum which is attached to the front of the underside of the head. The details of structure of the rostrum differ in different Hemiptera but agree in general plan (Fig. 160). The outside of the 168 THE HEMIPTERA 169 rostrum is a sheath which appears in the main to be derived from the labium or hinder hp of the chewing insect, being much elongated, and its sides rolled forward to meet or almost meet in front, forming a tube. The front part of this tube, however, near the head, seems not to be formed by the labium, leaving open a somewhat triangular place and the labrum or front lip appears to have grown downward to more or less completely close up this portion of the sheath. Within the tube .Mid ^-la Fig. 159. Fig. 160. Fig. 159. — Side view of a Squash Bug {Anasa tristis De G.) showing the rostrum, and its attachmentto the front of the head. Some of the mouth parts usually within the sheath have been pulled out and show in front of it. Rather more than twice natural size. {Original.) Fig. 160. — Diagram of a cross-section of rostrum of a Squash Bug: la, labium; md, mandible; mx, maxilla: Sa, tube carrying saliva to the wound; su, tube through which the food is drawn into the body. (Modified from Tower, Am. Ent. Soc. Am. VI, 1913.) thus formed lie the mandibles and maxillae which have become trans- formed into long and slender bristles with pointed tips. The surfaces of the maxillae which face each other have so changed their outline as to form two gutters or troughs and when the maxillae are pressed together as is the case in the living insect, each gutter of one side coincides with the corresponding one of the other to form two tubes, half of each being contributed by each maxilla. The more anterior of the tubes is for suck- ing the nourishment obtained, into the bug, while the other is for inject- ing saliva into the wound. The mandibles lie beside the maxillae and seem to function chiefly as piercing organs. In feeding, the tip of the rostrum is brought into contact with the sur- face of the object to be fed upon and the tips of the mandibles and maxillae are then driven into it until sap or blood as the case may be, is reached. Then saliva is forced into the wound and this seems to be irritating or even poisonous in its nature and its presence in the wound causes (in animals at least) an increased flow of the body fluids to that point. Assured thus of a sufficient supply of food, sucking it into the body of the insect is then begun. The eggs of Hemiptera are laid under greatly differing conditions. Some are inserted in twigs or stems; others are laid either singly or in 170 APPLIED ENTOMOLOGY clusters on leaves, twigs or in other places. The eggs themselves vary much in appearance, some being provided with circlets of spines, some with long filaments and some being smooth but of unusual form or color. They hatch into nymphs (Fig. 161) more or less closely resembling the adult, which stage they reach by a series of molts, changing with each molt. The Order Hemiptera may be characterized as: Insects which when adult nearly always have four wings, the front pair in most cases partly horny, partly membranous: with a plate located between the bases of the wings, usually triangidar in outline, in some cases covering more or less of the abdomen above: 7nouth parts for sucking, and attached to the front end of the underside of the head. Metamorphosis incomplete. Fig. 161. — Metamorphosis of the Squash Bug {Anasa tristis De G.) : adult and nymphs of different ages, all twice natural size. (From Fohom.) Hemiptera occur under almost every conceivable condition of life. Some live in water, coming to the surface only to obtain air: some are found on the surface of the water and some are found on the ocean hun- dreds of miles from land. Most of the group are terrestrial, however, and in many cases are widely distributed. Probably fifteen thousand species are already known but the group has been little studied as compared with some of the more attractively colored and marked orders. Those living in water are at least for the most part, feeders on insects and other animals small enough for them to capture : those which live on the surface are also predaceous, while of the land forms some consume other insects but probably the larger number are plant feeders. The Hemiptera are the true bugs, the general use of the term "bug" as applied to all insects being incorrect. THE HEMTPTERA 171 Family Pentatomida.-This group consists of land forms, many of them producing a disrtgreoable odor which has resulted m applying to these insects the common name "stink bugs" (Fig. 162). Most of them suck the sap from various plants, leaving behind the odor so often noticeable on berries. Others are carnivorous, attackmg caterpillars and sucking their juices. Many of them are minor pests and potentially important ones, and their fair size-often half an inch or more in length- together with considerable width, giving them a broad surface, makes them fairly familiar objects. Fig. 162. Fi«- 163. Fig. 164. Fig. 162.-Pentatomid Bug (£-/sc/iis<«s). natural size. iOriginal.) en,^j.ged Fig. 163.-Adult Harlequin Bug {Murgantia hzslriomca Hahn.), slightly enlarged ^"'"/ir'lU.-Eggs of Harlequin Bug, slightly enlarged. Modified from Essig. InJ. and Benef. Ins. Cal.) The Harlequin Bug {Murgantia histrionica Hahn).— This pest, native to Mexico and Central America, has gradually spread northward, feeding on cabbage, kale, mustard, turnip, radish and other crucifeTOUs plants, and its present northern limits are now in New Jersey and Long Island, Ohio, Indiana, Wisconsin, Iowa, Nebraska, Colorado, Arizona, Nevada and Washington, though the insect rarely does much injury so ^' The adults (Fig. 163) are about half an inch long, black or dark blue with bright red or orange marks, the brilliancy of the colors making the insects very noticeable and resulting in the common names calico- back," "terrapin-bug" and perhaps "fire-bug" as well. They winter in the adult stage under rubbish or wherever they can find protec ion, though in the far South they are more or less active nearly all the time and there the nymphs are also present then. Farther north the bugs become active during the early spnng and attack various wild cruciferous plants and lay their eggs (Fig. 164). These are usually placed in clusters of about 12, in two rows, and are somewhat barrel-shaped, white, with two black rings around each, and a third ring on the upper end, being both very noticeable and distmctive. They hatch in from 3 to 11 days according to the temperature and the nymphs suck the sap from the plants for 1 to 2 months, again according 172 APPLIED ENTOMOLOGY to the temperature, before becoming adult. When cabbage, cauhflower, kale, turnip, radish, etc., become available, the bugs go to these and there- after devote their attention to these plants until late in the fall when various other kinds, such as egg plant, asparagus, tomato, beans, beets, etc., may be attacked. Control. — Insecticides which do not injure the plants the bugs are on, are not usually effective against this pest and preventive methods have thus far given the best results. Planting a very early crop of kale, mustard or rape, to which the bugs when they first become active in spring may be attracted, is a good practice, for the insects seem to prefer these to the other plants. Here the bugs may be killed by spraying with kerosene, collected in nets and destroyed, or may be burned with a torch. The few that may escape this treatment can be picked by hand wherever found, but if the trapping method above is followed, few usually escape. Clean culture is also helpful. As soon as the crops are gathered all the stalks and leaves of the plants on which the Harlequin bug feeds should be gathered and destroyed, both to leave them no food and to remove possible places where they might winter. Rubbish which might provide wintering quarters should also be carefully removed. Recent tests with contact insecticides show some possibility that control by these materials may be obtained, but this subject has not yet been suffi- ciently investigated to warrant definite recommendations. Family Cydnidae. — The bugs of this family are usually of little eco- nomic importance. Some of them are interesting, however, as in them the scutellum, usually quite small, becomes greatly enlarged, covering nearly all of the thorax and abdomen behind the pronotum. In one genus the insects are nearly circular in outline, very convex, having much the form of lady beetles, and are generally glistening black, in a few cases with a narrow line of white. These are often called "negro-bugs" and one species feeds on small fruits and leaves a disagreeable odor. Family Coreidae. — Many of the members of this large family are of considerable size for bugs, some being over an inch long, but their bodies are much more narrow in proportion to their length than in the Penta- tomidse. Some of the southern species have broad, flat expansions of the tibiae, giving them a curious appearance. The insects of this group suck plant juices and a number are frequently more or less injurious to various plants. The Squash Bug {Anasa tristis De G.). — The Squash Bug is common almost everywhere in the United States feeding on squash and pumpkin and sometimes on cucumber and melon plants (see Fig. 161). The adult is a dark brown bug, very finely mottled with gray or lighter brown in many cases, about three-quarters of an inch long. It winters as the adult under rubbish or in other protected places, and appears in spring, ready for its food plants when these come up. When the leaves of the THE HEMIPTERA 173 plants develop the bugs lay their eggs on their under surface in clusters which vary greatly in the number of eggs composing them. The eggs themselves are oval in outline, very convex, and being resin-brown in color are very conspicuous against the green background of the leaf. In a cluster the eggs are not usually so laid that they touch, but somewhat spaced apart in most cases. At intervals before and during the egg- laying period the adults feed on the plants and when they are very abun- dant may seriously injure or in some cases even kill them. The eggs hatch on an average in about 10 days and the tiny nymphs, green and reddish in color, begin to suck the sap from the under side of the leaves, at first together, but scattering later. The reddish color of the nymph quickly changes to black and the green gradually becomes more of a gray. Feeding and molting five times results in the production of the adult after a period of from 4 to 5 weeks from the time the eggs hatch, and in the North the adults feed on the plants until fall; then go into winter quarters. In the South the longer seasons which permit an earlier start in the spring and the higher temperature which causes the eggs to hatch more quickly, permit the production, in some cases at least, of two generations each season. The injury to the plants caused by the spring feeding of the adult is continued by the sucking of the young. Where these are plenty, growth is checked and the crop reduced. If the plants are killed by frost before the nymphs are mature, they often attack the fruits in order to obtain the nourishment they need to become adult. Control. — Contact insecticides are not effective for the adult Squash bug, which has an unusually thick shell. The usual methods for control are the removal as far as possible of all rubbish and places where the insects can obtain protection during the winter; stimulation of growth of the plants by fertilizers and cultivation; protection of the young plants by fine netting until they are so well started that they can thrive despite the bugs; traps of bark or shingles placed close to the plants, under which the bugs gather at night and whence they can be gathered and destroyed early in the morning (this can be begun even before the plants are up) ; egg-masses being easily seen can be quickly found and crushed; and while the nymphs are small, spraying with Nicotine sulfate 40 per cent, 1 part in 400 of water will destroy them. The difficulty in reaching the nymphs on the under side of the leaves with the spray, can in part be obviated by attaching the nozzle of the spray pump to a piece of tubing connecting at its other end with the hose, and bent in a loop so as to give an upward spray. In the South one or two very closely allied species also attack the squashes and cucurbits and may be controlled in the same ways. Family Pyrrhocoridae. — The insects of this family superficially re- semble the Coreids and are of medium size. Only one is of any economic 174 APPLIED ENTOMOLOGY importance in the United States, and that in only a few of the Southern States though it is also injurious in some of the West India Islands. The Cotton Stainer (Dysdercus suturellus H.-S.) as it is called (Fig. 165), feeds on cotton, and occasionally the egg plant and orange among culti- vated crops. On oranges it attacks the fruit about the time it is ripen- ing, puncturing the skin and thus hastening decay. On cotton the insect punctures the partly developed bolls and if the attack is severe these may be destroyed. If not, the fiber is more or less stained, apparently from the punctures in the seeds, reducing the value of the cotton anywhere from 5 to 50 per cent. As the bugs develop in colonies and remain close together for some time and in their early stages are red, they Fig. 165. — The Cotton Stainer (Dysdercus suturellus H.-S.): a, nymph; b, Enlarged about three times. (From U. S. D. A. Farm. Bull. 890.) adult. are easily located and knocked off into dishes containing kerosene. In fall and spring they are attracted to baits, either of cottonseed or sugar cane, where they can be killed with kerosene. The bugs also feed and breed freely on Hibiscus and the Spanish Cocklebur, and the destruction of these plants near cotton fields will prevent their breeding there and spreading in larger numbers to the cotton. Family Lygaeidae. — There are many kinds of insects in this family but nearly all are small, being in most cases less than a third of an inch long. A number occasionally injure various plants, and one — the Chinch Bug — is one of the worst half-dozen pests in the United States. The Chinch Bug (Blissus leucopterus Say). — This little bug, less than a quarter of an inch long, feeds on all the grasses and cereal crops. It is apparently a native of tropical America which has migrated northward, THE HEMIPTERA 175 up the Atlantic Coast, the Mississippi Valley and the Pacific Coast, and is now found everywhere south of the St. Lawrence River and the Great Lakes and also in southern Ontario, Minnesota, Manitoba, the Dakotas and along the eastern slope of the Rocky Mountains to Texas. It has also been found in Arizona, California and Washington. It is not a serious pest usually in the northeastern states and many of the others, but in the Mississippi Valley it often destroys crops valued at a hundred million dollars, in one season. The adult luig (Fig. 166) is a tiny insect seemingly incapable of causing so much injury, but its enormous numbers make up for its small size. Fig. 166. — Different stages of the Chinch Bug {Blissus Icucoptcrus Say): a, nymph in first instar; b, fourth instar nymph; c, adult. All enlarged about nine times. {Modified from III. Agr. Exp. Sta. Bull. 95.) Its body is black or dark gray, with white and therefore conspicuous wings, each having a single black spot. There are two forms of adult, however, one with long, full-sized wings; the other with short wings only partially covering the top of the abdomen. The former occurs in the Mississippi Valley while the latter is met with, together with the long- winged form, in the Atlantic States and to some extent inland from there along the more southern of the Great Lakes to Illinois. The long-winged form passes the winter as the adult in grass tufts, under fallen leaves or in other places giving it protection. Corn shocks left out over winter often harbor enormous numbers. In spring the bugs leave their winter quarters and fly to the grain fields. Here they lay their eggs, several hundred in number, on the ground at the base of the plants or on the roots just below the surface, this process lasting about a month. The average length of the egg stage is about 2 weeks and the young which hatch, suck the sap from the plants for about 40 days before becoming adult. The nymphs are yellow with an orange tinge about in the middle of the abdomen. This soon spreads over the greater part 176 APPLIED ENTOMOLOGY of the body. In later stages the red becomes vermiHon, with a pale band across the front of the abdomen, the head and prothorax dusky and before becoming adult the red becomes quite dark. Development, at least for the individuals coming from the later eggs, is not complete before harvesting time, and to finish their growth they are obliged to migrate and find more food. They accordingly march in armies, often travelling some little distance on foot, and many which have already become adults, able to fly, march with them. In new feeding grounds development is completed and the eggs for a second generation are laid. This generation appears to feed more particularly on corn, kafir corn, millet and other, similar crops, and its members become adult before winter, and go into hiding until the following spring. With the short-winged form, hibernation at a distance from its food plant is impossible because of its inability to fly. This form therefore winters in grass-land and begins its work there in the spring. It is a question whether there is more than one generation a year for this form. Migrations when they occur, are of course on foot, and corn is no more liable to be attacked than timothy or any other grass crop. The Chinch Bug is particularly affected by weather conditions, dry weather being favorable, and wet seasons unfavorable. Dry weather appears to induce migration, and a succession of several dry years favors a large increase in their numbers and consequently of the injury they cause. Rains during the hatching periods of the eggs are very destructive to the insect, and the suppression of a Chinch Bug attack, anticipated because of the great abundance of the wintering bugs, by heavy rains at the right time in the spring is one reason why these pests are not even more serious than is the case. A fungus {Sporotrichu7n glohuliferum Speg.) generally called the "Chinch-bug Fungus" frequently attacks this insect, particularly during periods of wet, cool, cloudy weather, and then kills enormous numbers of them. In dry seasons it seems to have little effect, and attempts to control the Chinch Bug by placing individuals inoculated with the fungus in infested fields, while successful from the experimental stand- point, have on the whole, hardly produced the results hoped for. It is most valuable in seasons which are dry during the egg-hatching period but wet thereafter. In seasons then, when rains occur during the egg-hatching periods of the bugs, these and the fungus present will usually prevent serious outbreaks. In dry seasons, and particularly where there are several in succession, artificial methods of control must be resorted to. Control. — Numerous methods of control have been tested, with vary- ing degrees of success. Destruction of the adult bugs while wintering, has proved to be an efficient treatment when conditions are such as to make it reasonably complete. Burning over fields where the bugs are THE IIEMIPTERA 177 hidden in the grass has destroyed from about 50 to 75 per cent of them in cases where counts of the bugs could be made, including as well, how- ever, areas covered with weeds, fallen leaves and other rubbish. The difficulty with this treatment is to get weather conditions such that the burning can be well done and without injury to the grass. Where thickets, hedges and other excellent hibernating places which cannot be burned out are plenty, this treatment, while of value for the bugs in the areas where this method can be used, will of course fail to reach those in the other locations and thus leave many to appear in the spring. Where Chinch Bugs leave one field for another, an old practice has been to plow a furrow across their line of march and dig an occasional hole in the furrow into which the bugs, diverted from their first direction of march, might fall and be destroyed with oil or other material. Bands of tar or of road oil across their line of march have also been used with some success, the difficulty with this plan being in most cases that the band must be placed on firm, hard ground or it will soak in and need frequent renewal, besides forming (with some materials) a surface film on which the bugs can cross. Crude creosote similarly applied, has recently been found to work well. Though it soaks into the ground it appears to repel by its odor, and the bugs reaching the band turn away from it. Renewal is necessary only when the odor becomes so slight that it no longer acts as a repellent. In 1914 the average cost for material of maintaining a mile of this band during the migrating period of the bugs was only $16.50 at the then prevailing price of the creosote. When the Chinch Bugs are entering fields (usually corn) at this season, spraying the plants with kerosene emulsion. Nicotine sulfate 40 per cent and soap solutions has been tested. The former is liable to injure the plants if great care is not given to its application, but the tobacco extracts have proved satisfactory. Soap alone, used at the rate of 3 oz. per gallon of water has given excellent results, and while the Nicotine sulfate, using 3^^ fl. oz. in 1 gal. of water in which ]4, oz. of soap has been dissolved, may be the most effective, soap alone is likely to prove very satisfactory and is less costly. As the bugs enter corn fields from elsewhere, the spray need be applied only to the outer rows if the invasion is observed in time. The advice has also been given to cease planting corn in years when the Chinch Bugs are liable to be abundant, raising instead cowpeas, buckwheat, stock beets or soy beans, on which the bugs do not feed. In the case of the short-winged form there is little migration, and plowing and the rotation of crops where the insects appear, seems to be about the only treatment available, and probably all that will be necessary. 12 178 APPLIED ENTOMOLOGY That insects like other animals suffer from the attacks of various diseases, is perhaps not generally realized. Yet the list of these diseases is not a small one and our knowledge of them is still extremely limited. Some of them are caused by bacteria and are just as truly germ diseases as are those from which man suffers. Others are caused by parasitic plants which in one way or another enter the body of the insect and grow, consuming the nourishment they find there and finally kill the animal, usually making its body hard and firm, or "mummifying" it. A third type of disease is that known as the "wilt disease," in which neither bacteria nor fungi have been discovered, where the insect "wilts" after a time, becomes soft, and gradually decays. The producing cause of this class of diseases is still unknown, but they are infectious, spreading from one individual to another, and where the insects are abundant and weather conditions are favorable they cause a high mortality. Attempts have been made to utilize diseases for the control of insect pests. The Chinch Bug has been the subject of one of the most thorough of these experiments, the fungus already referred to having been cul- tivated for the purpose. It was found that by the use of appropriate methods, cultures of the fungus obtained in the fall could be grown during the winter, and bugs inoculated with it in the spring could be sent out to fields where the insects were abundant, and liberated there to spread the disease. To some extent this was a success, but it was soon found that if the inoculated bugs were set free during dry weather the disease failed to spread rapidly enough to prevent great injury, while if the weather was wet the fungus was in most cases already present and the addition of more diseased bugs at best only hastened its spread somewhat. As a business proposition then, the artificial cultivation and distribution of the fungus has been given up. In the case of a bacterial disease of grasshoppers which has at times been observed greatly to reduce the numbers of this insect, somewhat similar results have been obtained. In a few instances some degree of success has been secured by spreading the germs, but here the factor of cannibalism seems to enter into the problem. With species of grass- hoppers which feed considerably on dead or dying individuals, there is some probability of successful treatment in this way, but such species are not numerous, and there also appears to be more or less immunity to the germ in some species. The whole problem of control by disease appears to hinge on satis- factory answers to three questions: Can the disease be cultivated so that a supply can be obtained and continued? Can it be introduced successfully into regions where it is needed but not present? Will the disease establish itself there and become effective? The answers to the first two of these questions are liable to be affirma- tive ones, though this is not always the case. The third is the most THE HEMIPTERA 179 difficult to determine. It may be that the disease is not already present where it is desired to introduce it because conditions there are such that it will not thrive. Fungous diseases at least are influenced to a very large degree by the weather, most of them thriving best in warm, moist weather and if these conditions are not present they will amount to little. At the present time it would appear that the success of artificially introducing diseases to control insect attacks is so dependent upon weather conditions that man can do little more than supply the disease and trust that the needed kind of weather may follow. Unfortunately the very conditions under which injurious abundance of the insect takes place, appears in too many instances to be those distinctly unfavorable to the spread of the disease. Family Tingididae. — The insects (Fig. 167) of this family are delicate little bugs, usually having the pronotum broadly expanded and, with the Fig. 167. — Example of a Tingidid Bug (Gargaphia solani Heid.), enlarged about ten times (From U. S. D. A. Farm. Bull. 856.) hemielytra, covered with reticulated marks, giving them something the appearance of a bit of lace and this has been responsible for their com- mon name — lace-bugs. They are rarely more than an eighth of an inch long, usually whitish in color, and suck the sap from various plants, being generally found on the under side of the leaves. Their eggs are placed on the leaves, generally at the tops of small, brown, rather conical projections produced by the bugs, and which somewhat resemble places 180 APPLIED ENTOMOLOGY where fungi project from the leaf surface. Several species are occasion- ally rather injurious. Famihj Miridae. — This family until recently was called the Capsidse. It contains a very large number of species, perhaps more than any other family of bugs, all small, and all feeding on plant juices. Some feed on grass; others on succulent stems; some make a specialty, at least at cer- tain seasons, of sucking the sap from leaf and flower buds, distorting them or even preventing their development. Sometimes they are present in great numbers and do much injury. Fruit is attacked by some species, while it is small and rapidly growing, and such attacks produce "dimples" or small depressed areas, or they may even deform and thus greatly reduce the value of the fruit. Many secondary and potential pests belong in this family. Some of the adults are bright red; others red and black, yellow and black or other colors. In those feeding on grass, grayish-yellow or greenish-yellow is a frequent color. In many cases it seems that this is in some way connected with the color of their food, as for example, some species found on the stems of the red dogwood are them- selves largely red, though in other cases it is difficult to discover any such correspondence of color between the insect and its food plant. The Meadow Plant-bug {Miris dolohratus L.). — This is apparently a species introduced from Europe about a hundred years ago and now found over the eastern United States and as far west and south as Minnesota and Kentucky. It attacks cultivated grasses and is often extremely abundant. The adult (Fig. 168) is a rather slender bug about two-fifths of an inch long, with quite narrow wings. It is or yellowish-gray with darker markings and has long, black Fig. 168. — Meadow Plant-bug {Miris dolohratus L.), nearly twice natural size. {Original.) gray antennae. The eggs are laid in late summer and fall in grass stems, for the most part below the cutting level. They hatch the following spring and the nymphs feed on the sap of the plant stems for a little over a month before becoming adult. Many of the adults have short wings, a similar condition to that found in the chinch bug, but here the two forms mingle everywhere, though the short-winged individuals may make up as much as 90 per cent of the total number. Control. — Wintering in the egg stage in grass stems suggests the possibility of destroying many of the insects by burning over grass fields and particularly places where the grass was not cut, during the winter season. Early and close cutting of the fields might leave the insects little to feed on. Fall pasturing of the fields and the cultivation of sod THE HEMIPTERA 181 land found heavily infested may be of assistance, but so far, little or nothing has boon done to combat this pest. The Tarnished Plant-bug {Lygus pratensisL.). — The Tarnished Plant- bug is widely distributed, both in Europe and this country. It is about a quarter of an inch long (Fig. 169), shorter and broader in proportion than the Meadow Plant-bug, and varies greatly in its coloration. The general color, however, is brown, variegated with shades of yellowish and brown- ish and with black spots in some places. This pest feeds on over 50 different kinds of plants which are of value to man. The adults attack apple, pear, peach, and in fact all fruit tree buds, destroying or at least seriously injuring them: small fruits are often stunted or "buttoned" by them: flower buds of such plants as the chrysanthemum, dahlia, peony and aster are punctured and de- stroyed or malformed: potato leaves are often injured, causing tip-burn, and beets, particularly sugar beets, have their leaves curled and injured. ^ 1 i i 1 ii • Fig. 109. — Tarnished PI ant- bus Corn, wheat, oats and other gram (Lygus pratensis L.) -. a, adult; 6, nearly and grass crops are also injured by full-grown nymph. Nearly four times ., . • r 1 ■\TT•J^^ natural size. (From U. S. D. A. Farm. this omnivorous leeder. With young ^^^ll ggg j peach trees in nurseries it causes the trouble called "stop-back" by killing the terminal buds, and it is a cari'ier of the fire-blight of the pear, convoj'ing the bacteria causing this disease from infected to healthy trees. It is therefore a serious pest. The insect passes the winter as the adult and possibly as the nearly full-grown nymph also, in protected places, and appears with the first warm spring days and attacks the buds of fruit trees and other plants. Its eggs are inserted in leaf veins and stems, flowers and similar places, and they hatch in about 10 days. The nymphs feed on the juices of the plants and become adult in from 3 weeks to a month. There is therefore, time for several generations in a season, though the actual number of these does not appear to have been worked out and probably varies somewhat according to the length of the season in different parts of the country. Control. — No effective method of control has as yet been discovered for this pest, though many have been tried. Spraying the plants infested, with kerosene emulsion. Nicotine sulfate or soaps, early in the morning has been found to kill some of them. Shields covered with sticky fly- paper, placed beside and over the plants which are then jarred, captures some: the destruction of all wild plants such as asters and goldenrod on which they feed and breed has been advocated ; and growing plants under cheese-cloth; driving the insects down the wind, and other methods have been suggested, but no really efficient control is yet known. 182 APPLIED ENTOMOLOGY Family Phymatidae. — The Ambush-bugs (Fig. 170) as members of this family are called are carnivorous bugs which usually hide in blossoms to capture insects visiting there. They are rather short and stout, generally less than half an inch long, and have colors so combined on their bodies as to render them very inconspicuous in the flowers. Their prey is generally any insect they can grasp with their stout fore legs, whether it be injurious or otherwise. Fig. 170. Fig. 171. Fig. 170. — Ambush-bug {Phyinata erosa wolffii Stal.): a, from iibove; b, from the side, showing the grasping front leg. Enlarged: true length shown by hair line. (Modified from Sanderson and Jackson, Elementary Entomology, after Riley, U. S. D. A.) Fig. 171. — Reduviid Bug, about natural size. (Original.) Family Reduviidae. — This large family consists of carnivorous insects some of which are small while others are considerably more than an inch long (Fig. 171). Though generally feeding on the blood of other insects they may occasionally attack man and in such cases produce rather painful wounds. One species, most common in the Southern States, often enters houses and feeds upon the bedbug, and from this habit has been called the Masked Bedbug Hunter, the mask referring to dust which adheres to its rather sticky body before it l:)ecomes adult. Another species in the West and South is occasionally found in })eds where it imitates the habits of the true bedbug. A similar but different species occurs in California. The group as a whole, preying as its members do upon other insects almost entirely, must be regarded as a beneficial one. The family is most abundant in the warmer climates. Family Cimicidae. — The Cimicida3 is a very small group but well known through one of its members, the Bedbug. All of the insects belonging here are small, rather oval in outline, very flat, and rather i-eddish in color. Birds, poultry and bats are attacked by species similar to but smaller than the Bedbug and some of these under unusual condi- tions, may enter houses and attack man. The Bedbug {Civiex ledularius L.). — This universally distributed and well-known pest (Fig. 172) appears to have originated in Asia and has now spread wherever man is found. It is a small, flat insect, reddish- brown in color, about a fifth of an inch long when adult, and wingless, THE HEMIPTERA 183 only tiny stubs of wings remaining to show that it has been derived from winged ancestors. It produces a very noticeable odor. It is a nocturnal animal, hiding during the day in any cracks and crevices it may find, either in the bedstead, behind loose wall paper or elsewhere. In these places it lays its eggs, probal)ly about 200 in num- ber, these hatching in from a week to a much longer period dependent upon the temperature. The nymphs are yellowish-white at first, turning brown gradually with increasing age. Nymphal life varies greatly in its length, being affected by the temperature and food supply, but when these are favor- able, about 7 weeks is required to produce the adult bug. Under less favoring circumstances the nymphs may remain unchanged but ahve, for a long period. The number of genera- tions in a year may therefore differ greatly under different conditions but in warmed houses there are probably at least four. Where human blood is not obtainable for food, that of mice, rats or other animals where available, may be taken instead, and hving bedbugs in empty houses may perhaps be accounted for in this way. Without food, however, death within a year is a practical certainty. The "bite" of the bedbug is quite poison- ous to some persons l)ut not to others and in some cases a sort of immunity is obtained by individuals continuously exposed to attacks. Bedbugs are known to be carriers of contagious diseases of man, such as the African relapsing, fever, Kala-azar, plague, and possibly leprosy also, but of course the insect must first become itself infected with the causal agent of the disease which is very rarely the case, at least in the United States. It does not appear to transmit the diseases except as the agents of them by accident get on the mouth parts of the insect. Control. — Where sulfur can be burned in a room, using a pound for each 1,000 cu. ft. of space for 24 hr. the fumes will destroy all stages of the l^edbug if the room is reasonably tight. A thorough treatment of all places where the insects can hide and lay their eggs, with gasoline, benzine or kerosene is also successful if the material penetrates all parts of the cracks. Corrosive sublimate at least as strong as a 6 per cent water solution, can be used in the same way. Heating a room or house to from 120 to 130°F. in summer for an hour or even less has proved effective, as has a tempera- ture below 32°F. continued for 3 or 4 weeks. Persons obliged to stop at infested places can usually obtain protection by dusting insect powder (Pyrethrum) between the sheets of the bed. Fig. 172. — Adult female Bedbug {Cimex lectularius L.) gorged with blood. Greatly enlarged. {From U. S. D. A. Farm. Bull. 754.) 184 APPLIED ENTOMOLOGY Family Gerridae. — These insects, the Water Skaters or Water Striders (Fig. 173) as they are commonly called, are often noticed during the summer, skating over the surface of quiet pools of water. Their bodies are slender in most cases, less than half an inch long, usually black or brown, and their long, slender legs project some distance from the body. A few are shorter and broader bodied. They feed on any small insects they are able to capture and winter either under sticks or stones under water, or in mud near the edge, under leaves and rubbish. A few live on the surface of the ocean in warm climates. They are interesting insects to watch but are of little if any economic importance. Family Notonectidae. — The Back- swimmers (Fig. 174) as they are termed, live in fresh water. They Fig. 173. Fig. 174. Fig. 173. — Water Skater {Gerris conformis Uhl.) about natural size. {Original.) Fig. 174. — Notonectids and Corixid: A, Notonectid at the surface of the water showing under surface; A', swimming showing upper surface; B, Corixid swimming. Somewhat enlarged. {From Linville and Kelly, Text-book in General Zoology.) are small, rarely more than half an inch in length and generally black and cream-colored. The back has sloping sides something like the bottom of a })oat and they swim on their backs, propelling themselves by their long legs which are fringed with hairs. They occasionally come to the surface for air, a supply of which they carry down with them under their wings and between the fine hairs covering the under side of the body. They are carnivorous, feeding on other small insects but are of little importance. Family Corixid ae. — Living in the same places and with similar habits to the Back-swimmers are small, greenish and blackish mottled insects, rather oval in outline with heads somewhat flattened in front, and known as Water-boatmen (Fig. 174jB). They have long, fringed, oar-like legs but do not swim on their backs and in some way are able to reihain under water without coming up for air for a much longer time than the back- THE HEMIPTERA 185 swimmers. Like the latter group they often leave the water and fly at night and are frequently attracted to lights. Family Nepidae. — The water-scorpions as these insects are called, live in fresh-water ponds and pools. Two types of form are included, Fig. 175 Fig. 176. Fig. 175. — Water-scorpion {Ranalra americana Montd.) about natural size. {Original.) Fig. 176. — Giant Water- bug (Lethocerus americanus Leidy), natural size. {Original.) one having a long, slender body and long legs (Fig. 175), the front pair of which, unusually long, are constructed for grasping their prey which consists of small insects. In the other type the body is short, rather broad, and flat. In both a long tube consisting of two pieces which can be pressed together to form the tube, joins the hinder end of the body and while the insect is an inch under water in , some cases, this tube is pointed upward until its tip is out of water and through it the insect obtains air. The slender forms lying quiet on the bottom of pools resemble dead twigs and thus obtain the concealment needed to enable them to get within reach of their food. Family Belostomidae. — These insects are gen- erally termed the giant water-bugs. Some of them are the largest members of the Hemiptera, being two, three or more inches long, broad, flat and brown in color (Fig. 176). They live in fresh water and feed on insects and even small fish and are thus sometimes injurious in the production of food fishes. They fly by night and are frequently attracted to electric lights, which has led to the larger species being sometimes called "electric-light bugs." In some of the smaller species (Fig. 177) the eggs are laid on the back of the male who is thus obliged to carry them around until they hatch. Fig. 177. — Male Belostomid {Belostoma flumineum Say) carry- ing eggs on its back. Natural size. {Orig- inal.) CHAPTER XXVI THE HOMOPTERA The Homoptera is a large group containing insects of many forms, often sliowing little resemblance to one another. They suck sap from plants through a beak, apparently very similar in structure to that al- ready described for the Hemiptera, but it is attached, not to the front but to the hinder part of the under surface of the head which is very closely joined to the prothorax so that the beak frequently appears to arise between the front legs. In some instances where the adults do not feed, this structure is lacking. The wings are often absent but when present are usually held, while at rest, sloping over the body like a house roof. They are of the same thickness and usually, though not always, trans- parent. In this group (except the male scale insects) the metamorphosis is incomplete. These facts may be summarized as follows: The Homoptera are sucking insects with the beak {when present) arising from the hack part of the under side of the head which is very closely joined to the prothorax. The wings {frequently absent) are of uniform thickness throughout and when not in use are held sloping over the body. The meta- morphosis {except in male scale insects) is incomplete. Few groups of insects show as great differences in their members as are found here. The cicadas, often two or three inches in length and with a wing spread of four inches or more, are among the giants of the order, while some of the white flies and scale insects are hardly more than just visible to the eye. Most of the group move about freely, though some locate in one place soon after they hatch and remain there the rest of their lives. In one section the insect produces a protec- tive scale which covers it, and beneath this, degeneration of some parts of the body occurs. Many Homoptera secrete a sweet, sticky fluid called honey-dew, often in such quantities when the insects are in abundance, that in falling it makes a noise like fine rain. Striking on leaves, fruit or bark, it adheres and dries, and a blackish fungus grows in it, giving to such places a sooty appearance. This secretion appears to be produced most abundantly by the soft scales, white flies, plant lice, jumping plant Hce and some of the tree hoppers. Ants and honey bees feed on the honey-dew and frequently visit the insects producing it, for this food. Nine families of Homoptera are generally recognized, but four of 186 THE HOMOPTERA 187 these may, for convenience, be combined here. The six to be considered therefore are: Cicadas (Cicadida;). Leaf Hoppers and Tree Hoppers (four families). Jumping Plant Lice (Chermidai). Plant Lice (Aphidida>). White Flies (Aleyrodida^. Scale Insects (Coccidai). Order Homoptera ' Family CicadidaB (The Cicadas). — Most of the members of this family are rather large insects, with bodies often two or three inches or even more in length and quite stout as well. Their wings are correspondingly large, and in some species have a spread of more than six inches. Though usually transparent and with prominent veins they sometimes have pigmented areas of various colors. The adults place their eggs in slits they make with their ovipositors in twigs. On hatching the nymphs drop to the ground and make their way to the roots where they feed on the sap. Metamorphosis is more nearlj^ a complete one than in the other families of Homoptera (except the scales), the nymph having but little resemblance to the adult, and the last two nymphal stages are rather transitional in appearance between the two. The adult males have vocal organs located on the under side of the basal segments of the abdomen and covered by extensions backward of the metathorax. The sound produced is often so loud, especially when the insects are abundant, as to be very noticeable and even unpleasant. No auditory organ has as yet been discovered with certainty, in either sex. Cicadas are particularly inhabitants of warm countries, though some species are abundant quite far from these regions. In North America they occur in Canada and probably in all the States farther south, and are found as far north as England in the Old World. They are often wrongly called locusts. The Periodical Cicada or Seventeen- year Locust {Tibicina septendecim Say). — This remarkable insect is a native of North America. It is foimd from Mass- achusetts to Northern Florida and west to Wisconsin, Iowa, Kansas, Oklahoma and Texas, but is much less important near its northern limits than near the center of its range. The adult (Fig. 178) is about an inch long, with a stout, black body, orange eyes, legs and wing veins. The wings when at rest extend consid- ^^m ^ '^ ^■"^ Fig. 17 i Fig. 195. — Grape root showing galls caused by Phylloxera. {From Berlese.) ing spring. Then they attack the roots, forming swellings (Fig. 195) which on young rootlets stop their growth, and on the larger ones cause decay which spreads around the root and kills it beyond that point. THE HOMOPTERA 203 During the latter part of this second season some winged forms (Fig. 194) are produced and these make their way up to the surface of the ground and migrate to other vines where they lay eggs. These produce both male and female plant lice and each female lays a single fertilized egg which winters over. This 2 year life and the production of leaf galls is not always necessary to the continued existence of the insect however. The root form generally goes on, brood after brood, particularly on the European grape, without the formation of leaf galls, and while young from the leaves may probably pass to the roots at any time during the summer, the migration of root forms to the leaves is unknown. Apparently then, the life history just outlined applies to American varieties of the vine, but in the case of the European species, while the lice may pass to the roots they do not usually, at least, seem to migrate in the reverse direction, the insects coming from fertihzed eggs passing directly to the roots. Root forms may spread to other plants through the soil. Control. — -Four methods of control have been made use of for this pest, viz., the injection of Carbon disulfid into the soil close to the roots; flooding the vine- yard with water; planting in very sandy soils; arid the selection of resistant varieties. The first of these has given fair results where the soil is loose, deep and rich, but is most successful in cooler locations, and here the insect is least abun- dant. It is also rather expensive and has therefore largely l)een replaced Ijy other treatments. Submersion of the ground under water is a better method, but obviously cannot be made use of in most cases. The vineyard must be kept covered with at least six inches of water in order to drown the lice and unfortunately the l)est time to do this is during the summer when the vines are most liable to be injured by this treatment. The time chosen therefore, is after the vines have stopped active growth but before the lice have become dormant. In California this is generally some time in October. Flooding then should last from a week to 10 days: later in the season it must be extended and in the winter months 35 to 40 days of treatment is necessary. Planting in sandy soil is, for some reason not understood, a protection of the vines against Phylloxera, particularly where it contains a high percentage of siliceous sand. It is not always possible to locate vinej^ards on such soil however. The selection of resistant varieties of the grape is now the favored method of control. With such varieties the insects when present on the roots do not in- crease rapidly and the diseased tissue of the swellings on the roots does not go deeper than the bark, leaving the roots proper quite healthy. At the present time the grafting of vinifera varieties on resistant stalks which preserves the resistant properties of the roots while producing the vinifera quality of grapes so much desired, seems to give the best results in vineyards, though the proper combination of different varieties of the two calls for a detailed knowledge of the sul:)ject in actual practice. The Corn Root Aphis (Aphis maidi-radicis Forbes). — This insect, though it can hardly be regarded as universally distributed through the United States, is both a serious pest of corn over a large area and because of its interesting rela- tion with ants, an interesting species. It appears to occur throughout the eastern United States as far west as South Dakota and Colorado and south to South Carolina, Louisiana and Texas, but its destructive work mainly covers the territory from New Jersey to South Carolina and west to the Mississippi River. 204 APPLIED ENTOMOLOGY The eggs of this aphid hatch early in spring and from 10 to 22 generations (Figs. 196 and 197) are produced during the season. As cool fall weather appears, a generation of sexual individuals (Fig. 198) appears and these lay eggs which pass the winter. During this season they may be found in the ground in nests of several kinds of ants but most frequently in those of the little brown ant, Lasius niger americanus. They are oval, black and glistening and are sometimes found in small piles in the nests of the ants. In cold weather the ants carry the eggs down below the frost and on warm days bring them up to warmer levels. In spring, when various weeds such as smartweed, begin to grow, the ants tunnel along the roots of these weeds and place the young lice as they hatch, on them to feed. Later, when corn roots become available the ants transfer the lice to them, where they and their descendants feed during the rest of the season. Winged migrants are produced after a generation or two and these individuals spreading, are taken to corn roots by ants which may find them. All summer and fall the ants care for the lice, taking them from one plant to another and collecting from them the honey-dew upon which the ants feed. In the fall when the eggs are laid these are gathered by the ants and stored in their nests over winter. Where the Corn Root Aphid is abundant it becomes a serious corn pest, dwarfing the corn and turning the leaves yellow or reddish and sometimes destroy- ing the plants, particularly when weather conditions are also unfavorable. Fig. 196.— Corn Root Aphis (Aphis maidi- radicis Forbes) ; wingless, viviparous female. Greatly enlarged. {From U. S. D. A. Bur. Ent. Bull. 85, Part VL) Fig. 197. — Winged, viviparous female of the Corn Root Aphis, greatly enlarged. U. S. D. A. Bur. Ent. Bull. 85, Part VI.) {From Control. — Rotation of crops is of much value as a control, for as the lice cannot migrate until their second generation, corn planted on land where they are not already present will get well started. Fertilization and frequent cultiva- THE IIOMOl'TERA 205 tion to produce vigorous growth will aid in this. The worst injuries are usually where corn is planted to follow corn and therefore where this pest is already present in the field from the preceding year. Any method which will destroy the nests of the ants which care for the lice will also be helpful, and deep plowing and harrowing both in late fall and early spring has proved of value for this purpose. Some plant lice attack evergreens and pro- duce rather soft, fleshy galls, generally at the bases of the outer shoots. These appear during the spring months and are of full size by mid- summer. They then dry and crack open, showing little cavities occupied by the plant lice which now leave the galls for other parts, either of the same or some other kind of tree, according to the species concerned. The gall formation interferes with the growth of the tree by preventing wholly or in part, the circulation of the sap in the shoot at the base of which the gall is located, and this results, by the death or checking of the growth, in trees which look thin rather than dense, and in some cases they may become worthless as lawn ornaments. In the East the spruce is often seriously injured in this way. Many kinds of plant lice often become seriously abundant for periods of 2 or 3 years, then disappear for a time. The Potato Plant louse, the Pea louse, the Beet-root louse. Cherry plant lice and others have all been destructive for a year or two at a time within the last decade, and similar outbreaks of these or others may be expected any year. Wherever it is possible, spraying thoroughly upon the first appearance of the lice, with Fig. 198. — Oviparous female of the Corn Root Aphis, greatly enlarged. {From. V. S. D.A.Bur. Knt. Bull. 85, Part VI.) Fig. 199. — Aphid parasite {Ly.'