Agricultural entomology for students, farmers, fruit-growers and gardeners

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AfiRICULTORAL ENTOMOLOGY

Preface

This book is designed to meet the needs of students and others who wish to learn something of insect life especially in relation to farm crops and livestock. The author assumes that the students who read it will have had some training in general biology and will have the guidance of teachers familiar with the subject in connection with adequate laboratory facilities and opportunities for field studies. The details of laboratory and field studies have not been included since these are easily supplied by the teacher. For those making individual studies there are many available books covering the technic of entomological work. A glossary has been included which covers the subject as presented in these pages and in most of the reports and bulletins that are likely to be consulted by the average student.

In order to make the scope of the book adequate it has been necessary to condense the matter to the most essential details, and to omit much that has value but which is not absolutely indispensable to the presentation of the important principles that concern the practice of economic entomology.

The author acknowledges his indebtedness to many sources of information which are too numerous to mention individually, but he is especially indebted to Dr. Howard, of the Bureau of Entomology, for the privilege of using the illustrations secured from his office and for suggestions; to iv PREFACE

Professors Washburn and Bruner for the loan of plates; to the Iowa Experiment Station for use of figures, and the Ohio Experiment Station for a number of photographs for original use here. Professors Hine, INIetcalf, Barrows, Mr. Kostir and Mr. Drake have assisted in reading manuscript and proof and have generously given the author the use of photographs and drawings.

H. O.

Columbus, Ohio, 1916.

Introduction

The recent rapid growth in the subject of Agricultural Entomology makes it a difficult matter to bring together a comprehensive statement that will cover all of its different phases in a thorough manner. Some idea of its growth may be indicated by the fact that instead of a single entomologist employed in the United States Department of Agriculture, as was the case forty years ago, there are now several hundred who are devoting their entire time to the investigation of entomological problems, practically all of which are related to agriculture.

A similar development of this work has taken place in the State Experiment Stations, and there are also State Entomological departments working in almost every State, and in many of them two or three different organizations, each with a large quota of workers.

Economic entomology in its wider sense covers all those phases of the subject which have to do with insects of importance in relation to mankind. The forms which have distinctly agricultural relation are so numerous and represent so completely all the different groups of insects that we are compelled to include a very general survey of the subject.

Some idea of the size of the group of insects and of its place in biological study may be secured from the statement 2 ^ (17)

18 INTRODUCTION

that there are now known and have been scientifically recognized and described something over three hundred thousand species of insects, a number which far surpasses that of all other groups of animals together. Furthermore, the immense numbers of individuals in each species and the great facility which they possess for migration and rapidity of increase make them a very dominant group of animals.

Not all insects, to be sure, have a direct importance to mankind, but there is so large a number that are very directly related to human interests in the way of destruction of property or menace to health that it is unnecessary to emphasize their importance. Many estimates have been attempted of the extent of loss of crops, livestock, forests, agricultural products, etc., and while none of these can be considered exact, it is increasingly evident that such estimates are conservative and in many cases the loss is greater than is recognized. One of the current estimates is that about 10 per cent, of the aggregate of farm crops in the United States is lost by insect attack, and if this be taken as an approximate proportion there is something like one billion dollars to be counted an economic loss from this source each year.

It must be admitted that the entomologist has not been able as yet to solve all of the problems of insect control. There will doubtless be many cases where a practical control of insects may not be reached for many years, but for a considerable number of the most common and serious pests it has been possible to discover methods by which a very large proportion of the loss can be prevented. One phase of entomological work, therefore, is the demonstration of these possibilities in order to secure a general adoption of control measures that have been proved successful.

While it is manifestly impossible to include in a small book any full discussion of the many phases of entomology, it is the purpose of this work to present a basis for the understanding of field observations, and especially for the understanding of the many articles relating to economic insects which are now appearing in Government and State pub-

INTRODUCTION 19

lications. Many of these publications are available and will be found to contain an immense store of information, much of it of very practical value, but its greatest utility will be found to rest upon some acquaintance with the general facts of insect life and insect habits. These are so dependent upon certain conditions of structure ajid development that acquaintance with some of the fundamental biological features of insect life are essential to the most effective utilization.

Formerly all of the arthropods, that is, all animals with jointed bodies and jointed appendages, were grouped under the head of insects, and even yet this term has a pretty wide application in popular usage, although it is seldom used now to cover as wide a range as formerly. The Arthropods, as a whole, include crustaceans, myriapods, arachnids, hexapods, or six-footed insects, and of these the airbreathing forms, all except the crustaceans, are still quite commonly treated as insects.

The Onychophora is a tropical group including peripatus, the most primitive of tracheate animals, and would on this basis be considered as falling next to the Crustacea.

The most generalized next to these, the myriapods, might be counted as possessing the greater number of insect-like characters. This group, however, does not include any forms that possess wings, but in the matter of antennae and the tracheal respiration they are closely associated with insects. The members of this group are, for the most part, of comparatively little economic importance. A few of the species included in the group of centipedes (Ckilopoda) are poisonous, and in tropical countries are of some importance on this account. The few species that occur in temperate regions have little importance except as they may feed upon other insects which occur under the litter at the surface of the ground.

One species, the house centipede, a peculiar long-legged creature, w^hich is occasionally found in cellars or around houses, usually where there is some dampness, is, however, of a certain amount of importance because of its feeding

INTRODUCTION

111)011 insects, and is looked ii})on as rather servieeahle in the destruction of flies. It is a quite ungainly looking creature,

Fig. 1. — Scutigera forceps: Adult — natural size. (From Marlatt, Div. Ent., U, S. Dept. Ag.)

with slender, flattened body, extremely long legs, and an apparent duplication of anterior and posterior ends. The millipedes (Diplopoda) are nearly cylindrical in

INTRODUCTION 21

shape, are recognized as having two pairs of legs to each apparent segment and there is usually a large number of segments, 40 to 100 or more, so that the name thousandy^

Fig. 2. — Scutigera forceps: a, newly hatched individual; 6, one of the legs of same; c, terminal segment of body showing undeveloped legs coiled up within — all enlarged. (After Marlatt. Div. Ent., U, S. Dept. Ag.)

legged worm is fairly descriptive. Most of these species are found in moist places and feed upon vegetable debris, but a few have been recorded as attacking vegetation, and one species has been credited with injuring seed corn.

Chapter II. Class Arachnida

In the strict technical sense the group Arachnida may be excluded from the Insecta, but in general usage, and to a large extent in entomological practice, these divisions are put together, and it seems desirable that the group should be given a place in any work dealing with the insects in general.

The group Arachnida includes spiders, scorpions, harvestmen, mites, ticks, etc., and is characterized by the presence of four pairs of legs, the absence of antennae and compound eyes, and the lack of distinct metamorphosis, although in certain groups there is a considerable change from the newly hatched or six-legged form to the mature eight-legged stage.

In general structure the Arachnida agree with other Arthropoda, but the head and thorax are usually merged into a cephalothorax separated from the abdomen by a more or less distinct stalk; in the Acarina, however, this separation is not marked and the body is without distinct separation of head, thorax, and abdomen.

The economic importance of the group depends upon their attacks upon certain crops, from the fact that many of the species, such as spiders and harvestmen, are uniformly predaceous and serve as important checks upon injurious species; while other forms, such as the mites and ticks, are parasitic upon domestic animals and man, and some of the species occupy a most important relationship as carriers of infectious diseases.

The subdivisions of the group are, for the most part, very well marked and represent ancient groups which have diverged quite widely from each other.

The scorpions (Scorpionida), mostly tropical in distribu- (22)

tion, are represented by fossils in early geological times, and are noted as possessing poison glands. They are recognized by the broad cephalothorax, a division of the abdomen into two portions, an anterior preabdomen of seven segments, and a slender hinder postabdomen of six segments, on the last one of which there is a large poison gland and sting. The sting is distinctly venomous and fatal to insects or smaller animals, but seldom serious in its effect on the human species.

The Pseudoscorpionida are minute forms resembling scorpions in the width of the body and the long pedipalps, but have no postabdomen or sting. They occur somewhat commonly under bark or decaying logs or occasionally in old papers or books, where they may secure book lice as food.

The Pedipalpi, or whip scorpions, have a tropical or subtropical distribution and differ from the preceding groups in the presence of a long, slender bristle or whip extending from the hinder abdominal segment.

In the group Solpugida there is an exceptional separation of head and thorax and the abdomen is distinctly segmented, while the chelicerse are greatly enlarged and strongly chelate. These are not only largely tropical, but are particularly characteristic of arid regions. One species occurs in the Rocky Mountain region as far north as Colorado. They are carnivorous in habit, but not of particular economic importance, as they occur usually in small numbers and in locations which do not offer opportunity to capture especially injurious insects.

The Phalangida, or harvestmen, often called "daddy-longlegs," are somewhat large and resemble spiders in appearance, but the abdomen is not distinctly separated from the thorax and the legs are in most species extremely long. They feed on insects, especially on flies and other small forms, and are to be counted as distinctly beneficial. On account of a strong pungent odor they are disagreeable to handle, but their presence in gardens and other places where insects abound may be considered as distinctly desirable.

Order ARANEIDA.

This jijroii]) includes tlie familiar s])i(lers which are very generally distributed over tlie world, and occupy a rather conspicuous place among other animals. Their body is sharply divided into cei)hal()th()rax and abdomen, and the four pairs of legs are usually nearly equal in length. The

Fig. .3. — Epeira scolopetaria, showdng normal position of spider in web head downward. A vibrator at x agitating the web will cause the spider to rush at once to point of contact. (Photo by Prof. W, M. Barrows.)

eyes are simple and usually eight in number, and the large mandibles are attached at right angles to the axis of the body. In some species these are provided with a poison duct. The })ite is venomous to smaller organisms, and in some of the larger, like the tarantula, the bite is a serious matter for man. Spiders oft'er a great many attractive features, particularly in their web-making habit and in their adaptation for the capture of prey. They are distinctly carnivorous in habit and may be considered useful, since the majority of them capture insects, and the kinds of insects captured are quite generally such as are detrimental to man. In general, therefore, spiders should be left unmolested and their insect-feeding habits utilized in the reduction of injurious insects.

Fig. 4. — The common red spider (Tetranychus bimaculatus) : a, adult; b, palpus; c, claws; a, greatly enlarged; h, c, still more enlarged. (After Banks. From Bur. Ent., U. S. Dept. Ag.)

Order ACARINA.

These are commonly known as mites, ticks, scab insects, mange insects, etc., and are in general distinguished by having no prominent separation between the different regions of the body, the head, thorax, and abdomen, forming one closely connected structure. They have eight legs, except in the early stages, when there are but six; the eyes are often small or obsolete, the spiracles reduced to one pair, sometimes apparently wanting; the mouth parts are fitted for piercing, biting, or in some cases for combined biting and suction, there being usually a pair of slender, sharp mandibles capable of penetrating the skin of the host animals. Much variation of habit exists, and ranges from free forms to strictly parasitic forms.

Fig. 5 — Tetranychus gloveri: Adult — much enlarged. (Titus, Div. Ent., U. S. Dept. Ag.)

Harvest Mites; Chiggers.

In the family TromhidiidoB, which includes normally plant-feeding species, we find a few species which have adopted a phase of parasitism which, though apparently abnormal, results in extreme annoyance to the animals affected.

Apparently the most abundant species in this country is the Leptus irritans of Riley, which is illustrated herewith. This occurs in a large portion of the United States, and occasions during the summer months an enormous amount of suffering. It ranges north in the Mississippi Valley into central Iowa, at least, and in Ohio to Lake Erie, appearing by the latter part of June or fore part of July, but becoming especially annoying during August. In the latitude of Washington it is very abundant early in June, and farther south its season extends until, in southern Mexico, what is apparently the same species is abundant and equally annoying in January.

The form in which this pest is observed usually is the larval or six-legged form. It is nearly circular in outline, the legs extending well beyond the margins of the body, of a bright red color, and so minute that it is only with the closest scrutiny that it can be detected.

Fig. 6. — Leptus irritans to the right and americana to the left. (From

Riley.)

It is brushed from the leaves of various plants on to the hands or clothing of people and to the bodies of other animals, and the mite then proceeds to burrow into the skin, notwithstanding the fact that, so far as all evidence shows, this proceeding is absolutely fatal to it and prevents any possibility of its maturing or producing eggs.

There is great difference in the susceptibility shown by different persons to the attacks of this mite, some not seeming to be affected seriously by them, while others must submit to extreme torture every time they happen to become attacked by them, even if but few in number.

As the mites are invariably secured })y working among raspberries, currants, or other sln-ub})ery wliicli luirbors them, or by walkin^^ in grass or low herbage wliere they occur, sometimes even by sitting or lying for a short time upon grass or clover, it is evident that the best precaution for suscej^tible ])ersons is to avoid all such ex])osure. When such avoidance is impracticable, the clothing may be made to fit closely at the wrists and ankles, and then as soon as possible after having been exposed to the mites make an entire change of clothing, bathe in hot, soapy water, and if any indications of mites are present, wash the affected ])arts with diluted carbolic acid, 1 part to 50 or 100 parts water.

In the tropics rum or w^hisky is recommended as a wash, and diluted alcohol can be used with good results.

With a little pains it is possible to locate the mites, as they may be found before they have completely buried themselves in the skin in the centre of the little red swelling that has been raised by their preliminary irritation, and if they are removed at this stage, instead of being allowed to bury themselves in the skin the subsequent inflammation and itching will be largely prevented.

Family Gamasidse. — The family Gamasidce contains a large number of small mites, most of them being free or semiparasitic in habit.

A large number occur as parasites on various species of insects, but the two species to be mentioned here occur on birds, and are sometimes very troublesome.

The Bird Tick (Dermanyssiis avium). — The bird tick is a very familiar form to keepers of cage birds, and is known in many places as the red mite. It occurs on a great variety of birds, and has sometimes been considered to embrace the chicken tick, mention of which follows, but that is now generally conceded to represent a distinct form. The mites are easily seen with the naked eye and appear as animated red specks running over the bodies of birds, or on the perches, bars of cages, etc. The eggs are laid in cracks or corners of the cage, where may be found also the molted skins and often numerous young and old mites.

The attacks on the birds are made probably for the most part at night, but the mites are usually well filled with blood, which gives them their red color.

The use of perches that are solid, smooth, and free from cracks, and the frequent dipping of these in hot water, and the thorough cleansing of the entire cage, using boiling water if there are inaccessible cracks, will serve to destroy the pests.

Fig. 7. — Poultry tick (Dermanyssus gallince): a, adult; 6, tarsus; c, mouth parts; d and e, young — all enlarged. (After Osborn, Bur. Ent., U. S. Dept. Ag.)

The Poultry Tick {Dermanyssus (jalUfKp). ^One of the most persistent and injurious of the pests of the hennery is the little chicken mite, which gathers on the fowls, especially at night, and sucks their blood. It is a well-known form, and has been described for many years, though in many works it is confused with the preceding species or considered simply a variety of that form. Its distribution seems to extend pretty generally over the world where domestic fowls are kept.

The full-grown mites are about 1 mm. long, of a light gray or wliitish color, with dark patches showing through the skin, but when full fed have a distinct red color. They swarm in cracks and corners of the henhouse, and often when numerous, over all surrounding objects, and at such time are liable to become a great pest to man and such other animals as they may get access to.

The dust bath is considered of use in checking this pest, but when there is a general infestation, the best plan will be found to clear the house, then spray well with kerosene or kerosene emulsion, taking pains to reach the cracks; thoroughly drench the roosts with hot water or kerosene, benzine, or gasoline, whitewash the house, or dust with carbolated lime, and then daub the ends of the roosts, where they come in contact with supports, with coal tar, so the mites w^ould have to cross it to reach the fowls.

Family Ixodidae. — This family includes forms known commonly as ticks, and familiar examples are the dog tick or wood tick, frequently found upon domestic animals, and other examples are the cattle tick of the Southern States and spotted fever tick of the Rocky Mountain region. In this group the body is robust and becomes much distended in the female when the eggs are developed. The mouth parts are adapted for puncturing the skin of host animals, and the species generally attach themselves to warm-blooded animals as 'a part of the life-cycle, and in some cases this attachment is permanent, while in others it is temporary and the individual tick may occupy several different hosts in the course of its life-cycle.

The family is of particular importance because of the fact that some of the species are carriers of important diseases, most notable of which is Texas fever, transmitted by the cattle tick. The spotted fever tick is the carrier of spotted fever.

The Pigeon Tick {Argas reflexus). — The pigeon tick is a common species on pigeons found mainly in pigeon houses, and sucks the blood of pigeons for its nutriment. It is, however, able to survive for long periods without food, some recorded instances are of individuals kept in confinement for two years without food, but which moulted at frequent intervals.

The related Argas persicus occurs both in the old world and America. It is a troublesome pest for chickens and is credited also with attacks on human beings.

Fig. 8.

-Argas miniatus, a tick which infests poultry. Greatly enlarged. (Banks, Div. Ent., U. S. Dept. Ag.)

The Cattle Tick (Margaropus annulatus). — The cattle tick, as already mentioned, has received probably more attention than any other species, as it has been known for many years as the carrier of Texas fever in cattle, and its great importance to the cattle industry has been the occasion for elaborate studies regarding its habits. In this species the newly hatched tick locates as soon as possible upon a warm-blooded animal, preferably upon cattle, as these seem to be by all means the preferred host. Once located they retain their attachment until mature. The females when mature and gorged with eggs loosen their hold, drop to the ground and eggs may be distributed wherever the adults fall. The period of incubation differs greatly, with regard to temperature, so that the rate of development and number of generations differ much at different seasons of the year. An important fact concerning tlie transfer of disease is that tlie protozoa in the diseased animal are taken into the l)ody of the tick, and within tlie body of this host may enter the eggs, so that young ticks that have never fed upon an animal may serve to introduce the parasite in an individual that has not previously had the disease.

Elimination of ticks from the cattle and prevention of their attacks therefore become essential factors in the eradication of Texas fever. To accomplish the eradication of the ticks in any given locality it is necessary to rotate animals from one field to another, allowing time for hatching of eggs and dying of the ticks before the field again is used as a pasture for cattle. Working upon this basis, considerable areas in the Southern States are now considered tick-free and the hope is that the quarantine line will be pushed farther and farther south until ultimately the ticks and associated disease may be completely eradicated. Certain districts in Tennessee and North Carolina are now considered tick-free and released from quarantine restrictions.

The Spotted Fever Tick {Dermacentor wnvsta). — The spotted fever tick has come into great prominence in recent years because of the determination that it serves as the carrier of the much-dreaded spotted fever. This disease has caused many deaths in Montana and adjacent States, and the rate of mortality for individuals attacked is very high, so that its appearance is very much dreaded.

It has been shown that this disease is carried by this particular species of tick, and in no other way. It differs in habit from the cattle tick in that a number of different hosts may be fed upon at different periods in its development. Usually the young larvae attach themselves to ground squirrels or smaller mammals and remain upon these from three to five days, after which they drop to the ground. After a resting period of from one to three weeks the skin is moulted and an eight-legged form appears, which in turn attaches itself to some host and feeds for several days, dropping to the ground and developing into the adult

OIWFlR ACARINA

Fig. 9

Fig. 10

Fig. 11

Fig. 12

Figs. 9 to 14. — The spotted fever tick {Dermacentor venustus and Dermacentor albipictus). (Hunter and Bishopp.) Fig. 9, adult spotted fever tick which has deposited eggs. Fig. 10, larva of spotted fever tick. Fig. 11, engorged nymph of spotted fever tick. Fig. 12, the same, ventral view. Fig. 13, adult male of Dermacentor albipictus. Fig. 14, adult female of Dermacentor albipictus, unengorged. 3 stage. In the adult stage still another host is sought, this time usually some of the larger animals, such as domestic cattle or sheep, and })robably in the wild condition such

Fig. lo.—Psoroptes communis, var. equi. (Reduced from Furstenberg, after Murray.)

animals as the antelope or Rocky Mountain sheep or other ruminants of the Rocky Mountain region. On these hosts fertilization occurs and the females then drop to the ground where the eggs are laid and a new cycle begun. The disease has some remarkable limitations in its distribution which are probably associated with the distribution of the ticks or the animals which serve as a reserve for the disease germs.

Family Sarcoptidse. — This family includes parasitic mites, affecting particularly birds and mammals.

The Sheep Scab Mite {Psoroptes communis, var. oms). — The sheep scab mite produces a very serious condition among sheep, evidenced by matting and tagging of wool and the formation of thick, encrusting scabs. The eggs of this mite are minute, glistening white specks, longer than broad and nearly uniform in thickness. They may be found under the scabs by careful inspection, and their detection, even when mites are not seen, may be taken as evidence of the disease.

The larvse have nearly the same shape as the adults, but are to be distinguished by the fact that only six legs are apparent.

The full-grown mites are nearly as broad as long, and are characterized by their piercing mouth parts and the structure of the two posterior pairs of legs (see Fig. 15). In the male the fourth is much reduced, and the third bears a long thread-like appendage passing the sucker, while in the female this leg carries two long, thread-like organs and no sucker.

The only treatment for this species worthy of recognition is that of dipping, and this, if properly done, will secure the extermination of the pest. A flock once freed will not become again infested except by exposure to infected animals or by the introduction of scabby individuals.

So important is this parasite deemed that many of the States have adopted stringent laws for the quarantine of infected animals and for prescribing dips that must be used.

The particular kind of dip is of less importance than the thorough use of the one selected. The tobacco dips, sulphur and lime dips, and also several of the patent dips prepared by reputable firms can be recommended. The main objection to the latter, perhaps, is the fact that the user must

CLASS A RA CIINI DA pay a rather ex()r})itant ])ri(*e for a few simple ehemicals, and further, in ease of the arsenieal dips, that lie ma\- not know the ingredients or their proportions and thereby endanuer the animals treated.

The Itch Mite. — The iteh mite, or " iteh inseet," affecting man is perhaps becoming a rather rare pest in civilized communities, but since it occurs at times on domestic animals, and in certain varieties becomes at times a serious pest to sucli animals, it deserves mention here. Authors

Fig. 16. — Sarcoptes ficabiei: male and female. Furstenberg, after Murray.)

(Reduced from have differed greatly in their treatment of the species, some making a different species for each host animal, believing that they could find distinctive characters in the size, arrangement of spines, etc.; but recent authors have combined most of these under the one species, scabiei, though in some cases retaining the varietal distinction for various hosts.

All stages of the parasite occur on the host upon which it is absolutely dependent for existence. Generation after generation may occur on the same animal. The mite burrows under th^ skin, in this respect differing from scab mites.

The adult mites are flattened, rather circular in outline, and may be separated from related forms by the character of the feet and by the presence of six short spines or thorns on the thoracic portion and fourteen on the abdominal portion of the body.

Eggs are deposited along the burrow as the mite extends its channel into the deeper portions of the skin, and as they hatch the young feed upon the surrounding tissues, and it is said moult four times before maturity. When fully grown they wander around and mate on the surface of the skin, after which the females begin a fresh burrow.

Infection with this parasite is accompanied by intense itching during the formation of pustules and inflamed areas, and while in man it is usually confined to the base of the fingers and between the knuckles, in aggravated cases the whole hand and arm may become invaded.