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Home , Diamphidia, Honey bee, Insect physiology, Mealworm

called mycetocytcs, for the bacteria to live in. A vinegar , melano- Life Processes gaster, has been reared under sterile conditions on a definite chemical me- of dium. It is the first multicelled - ism to be raised in the absence of Frank H. Bah er s ^ John J. Pratt ^ Jr. micro-organisms on a diet whose chem- ical composition was exactly known. Certain insects, such as mealworms, A study of can tell require little water because they can us a great deal about the phenomenon derive metabolic water from carbo- of life and help entomologists in their hydrates. fight against insect pests. The ability to utilize sugars varies Of especial interest is nutrition, for considerably. Mannose is used by blow the digestive systems of insects are as and vinegar flies but not by . diverse as the insects themselves and Only are able to use arabinose. the kinds of they eat. When all Vinegar flies can survive for long pe- the evidence on that complex subject is riods on a diet of pure , rafíi- in we will be that much closer to the nosc, or melezitosc. solution to some mysteries that still To grow, insects must have confront the biologist, physiologist, and or their equivalent. Some mature in- biochemist. sects can survive a long time on a pro- Some eat almost anything, tein-free diet, but they either undergo but some have a restricted diet. Some no further development in their adult Piave been given more than one com- stages or utilize food materials already mon name because they customarily stored in the body. Certain amino feed on more than one plant: Boll- acids, the building blocks of proteins, , fruitworm, and corn seem to be essential for proper growth earworm, for instance, are one insect. and development; the German cock- The influence of diet on the growth roach requires at least iivc, valine, is illustrated by the . Larvae tryptophane, histidine, arginine, and that are to become queens are fed on cystine. a diet of . Other larvae des- Ectoparasites such as lice seem to tined to become workers are fed on develop better on vitamin-deficient royal jelly for only 2 days and for the than on well-fed ones. When rest of their larval life receive honey human volunteers were fed for several and . months on a diet deficient in certain Several factors or vitamins are vitamins and then infested with lice, necessary for normal growth. The - however, the lice developed just as well soluble factors so important in mam- as they did on humans that had a com- malian physiology, except for choles- plete diet. On the other hand, it seems terol, apparently are not required by true that various insects often develop a number of insects. The water-soluble better and in greater numbers on plants factors do play an important role. Most with nutritional deficiencies than on species need the B vitamins. Vitamin well-fed plants. Powder-post C does not seem to be required, but at cannot digest cellulose. If allowed to least one insect, the cockroach, synthe- choose among pieces of oak sapwood sizes vitamin C. Symbionts are bacteria of diflercnt starch content, the female that are transmitted hereditarily from almost always chooses the wood with parent insect to offspring. Apparently the highest starch content in which to these bacteria are essential in the nu- lay her . trition of many insects. Sometimes the Metabolism is the sum of all the insects provide specialized structures. chemical and physical processes by

30 Life Processes of Insects 31 which living organized substance is processes. The oxygen consumption of produced and maintained. The subject cockroach muscle is about the same as obviously is complex and in only a few that of pigeon-breast muscle, which instances has the metabolism of an in- heretofore has been considered the gested food been followed completely. most active known. What happens to the blood pigment Besides the usual waste products of hemoglobin after it is ingested by metabolism, many insects excrete ma- bloodsucking has been in- terials like and , which they vestigated. In most of the insects stud- use for various purposes. Other sub- ied the bulk of hemoglobin seems to be stances, such as the fetid material ex- broken down in the gut to hcmatin, creted by stink bugs, are used for pro- which is then excreted unchanged. In tection. Still others, such as the venom mosquitoes and fleas, no pigment seems of the , are used in obtaining food. to be absorbed. In all the other forms, Radioactive amino acids have been pigment in varying amounts is ab- injected into the giant silkworm and sorbed and circulates in the hemo- apparently radioactive silk was ob- . In the louse the absorbed pig- tained. The studies will help explain ment is further broken down to the bile the chemical structure of silk. pigment, biliverdin, and in other The naturalist Athanasius Kircher species bilirubin is also found. in 1643 recommended music as an During , the period antidote for tarantula bites. Different during which the insect changes from treatments are used today for insect an immature stage to an adult, the de- bites, but often they are no more efTec- hydrogenase enzym.e activity in the tive than Kircher's. We know little blow fly falls rapidly at first, reaches a about the of insect venom. In minimum at about the halfway point some it is formic acid; in others, of the pupal period, then rises rapidly toxic . Bee venom is made up of and continuously until metamorphosis several toxic constituents, the chief of is completed. The acidity of the pupal which is . When it is injected fluid follows a somewhat différent by the sting of the bee, in the course, becoming strongly acid soon cause a breakdown of proto- after the beginning of metamorphosis, plasm and the liberation of histamine. and reaches a maximum, at about the It is this chemical that is responsible same time the dehydrogenase activity for many of the symptoms of . is lowest. The acidity then decreases Since early times bee venom often has until the time for emergence, when the been recommended for the treatment fluids are almost neutral. In the Japa- of arthritis, neuritis, and rheumatism. nese , the changes in fat and gly- Another mystery is the nature of the cogen content during metamorphosis salivary secretion of various mos- may indicate that the insect synthesized quitoes and flies. A toxic arrow glycogen from fat. used by the Bushmen of the Kalahari The metabolism of iodine by vinegar Desert in South is obtained from flics was studied by the use of radio- the of the beetle Diamphidia active iodine (P^^). When it was fed to locusta. larvae, the iodine was concentrated Insects do not have blood vessels. mostly in the protein of the skeletal The circulating fluid flows freely parts of the larvae. If the pupae formed throughout the body cavity except from larvae fed radioactive iodine were while it is being moved by the dorsal removed from the food before emer- vessel or heart. It corresponds to both gence, the adult insects did not contain blood and lymph and is called hemo- radioactive material. lymph. In some insects it is clear and The amount of oxygen consumed by colorless. In others it is yellow or green. tissues during metabolism is an indica- The volume varies greatly betv/een spe- tion of the activity of the metabolic cies and individuals of one species. The 32 Yearbook of Agriculture 1952 does not contain respira- Hemolymph from Japanese beetle tory pigments such as hemoglobin or grubs coagulates by a gelation of the hemocyanin. Many analyses of hemo- plasma, while that from the wax lymph have been made, but the func- coagulates by agglutination of the cells. tion of only a few of the many compo- The coagulation of the hemolymph nents has been determined. from these two species may be greatly Insect hemolymph contains more retarded by exposing the larvae to sub- free amino acids than does human lethal intensities of ultrasonic waves. blood, which averages about 6 milli- None of the chemicals normally used grams per hundred milliliters. Insect to prevent the clotting of mammalian blood may contain as high as 385 mil- blood has a similar elïect on insect ligrams per hundred milliliters. At blood. least 24 compounds with the chemical properties of amino acids that occur Tw^ENTY or more species of insects free in the hemolymph of insects have have developed resistance to insecti- been identified by the use of paper cides following exposure to Chromatographie methods. Several of under natural conditions. Resistant them have not been identified yet as strains have been developed in the lab- constituents of proteins. oratory by exposing many insects to In most insects the hemolymph con- concentrations of that killed tains a much higher percentage of po- 90 percent of them. Eggs from the sur- tassium than docs mammalian blood. vivors were used to maintain a . Among phytophagous, or plant-feed- The process was repeated with each ing insects, the sodium-potassium ratio generation. In a short time the off- is less than i ; among carnivorous in- spring showed considerable tolerance sects, the ratio is greater than i. Some for the insecticide used in the selective species of insects apparently have some process and also, usually, for many sort of sodium-potassium regulatory chemically unrelated compounds. system, because the ratio in the body The control of the wild resistant in- fluid is not dependent on the ratio in sects has become a serious problem— food. In the silkworm larva, the sodium DDT, after a few years of use, often concentration in the body fluid seems has failed to control house flies and to be in simple difl'usion equilibrium mosquitoes. Apparently no external with ingested sodium. Silkworm pupae diñ"erences exist between susceptible and adults contain almost no sodium. and insecticide-resistant flies. Scien- It therefore must be selectively ex- tists have tried to find out whether creted. there are physiological difl"crences. Insect hemolymph contains a num- They have yet found no significant dif- ber of cells, or hemocytes. Their most ference in vigor between susceptible obvious activity corresponds to that of ' and resistant strains : Resistance is not the leucocytes, or white blood corpus- due simply to the failure of the insecti- cles, of the in that they cide to penetrate the of the ingest any small particles of solid mat- insect, because the insects are also re- ter set free in the blood. Ten classes sistant when the insecticide is injected and 32 types of cells have been found directly into the body cavity. in the blood of the southern army- The cholinesterase rapidly worm, and 8 classes and 23 types of destroys actylcholine, a chemical of im- cells in the blood of the mealworm. portant function in the transmission of When removed from the insect, the impulses across the nerve-cell hemolymph of some species clots rap- junctions of several species. In idly and in others more slowly or not insects the role of cholinesterase has at all. The process of coagulation is not not been determined, but because of comparable to that of mammalian the high concentration of the enzyme blood and varies between insect species. in insect nerve tissue, it is of interest in Life Processes of Insects 33 the physiology of resistance to insecti- Most of the insect pigments were once cides. thought to be simple end products of The cholinesterase activity of the metabolism without physiological func- heads of resistant flies is less than that tion. We now know that this is not of normal flies. DDT applied exter- always correct. Before the physiological nally to house flies apparently is first function of the pigments was estab- absorbed and then metabolized. One lished, many were of commercial im- DDT-resistant strain was more able to portance. Carminic acid froin the metabolize DDT than were normal cochineal insect was used as a wool dye flies. By the use of large amounts of from early times until azo dyes were piperonyl cyclonene, the conversion of discovered. DDT to the metabolic product by the The tcrmi melanin is loosely applied resistant flies was largely prevented. to denote what is probably a group of Another strain of DDT-resistant flies pigments with varying composition. also rapidly metabolized DDT that The pigments appear to be derived had been absorbed. The main product from tyrosine, an , by a of metabolism was DDE (1,1 -dichloro- scries of enzymatic reactions. The dark- 2,2-bis-(/;-chlorophenyl) ethylene). A ening of insect blood on exposure to air small amount of DDA (bis-(/;-chloro- is also generally due to melanin forma- phenyl) acetic acid) was also identi- tion; the blood docs not darken in the fied. Only small amounts of the metab- insect because of the inhibition of the olites were excreted and large amounts enzymes by some unknown factor, pos- were retained in the body. In contrast sibly by a low oxidation-reduction po- to that strain, the normal, or DDT- tential. The of pigment susceptible, flics could metabolize only formation has thrown considerable a negligible amount of DDT in 24 light on the action of genes, the units hours; neither DDE nor DDA was a in the that carry the product of the metabolism. hereditary characters. Evidence has Gytochrome oxidase, an enzyme been presented that the process of me- found in cells, is of great importance lanin formation in mammalian tissues in the metabolic processes. The activity follows a similar pattern to that of in- of the enzyme was much greater in one sects. strain of resistant flies than in a normal The presence of hemoglobin in in- strain. sects is an interesting point because it We do not know whether the physio- does not ordinarily function in its tra- logical differences between resistant ditional role of oxygen carrier. In and susceptible strains are due to the midge larvae (Tendipedidae), such a resistance. They may be variations in function seems doubtful, even when the strain, due to differences in rearing oxygen tension is reduced greatly. The procedures or some other factor. active group of the hemoglobin found The rate of loss of tolerance to in- in bot fly {Gasterophilus) larvae is secticides following cessation of ex- the same as that in the hemoglobin of posure also seems to vary tremendously horse blood, but the protein part of the between strains. Some strains, whose complex is different. Its molecular resistance was developed either in the weight is about 34,000, compared to field or laboratory, revert rapidly to about 67,000 for human hemoglobin. nonresistant insects. Others retain re- Its affinity for carbon monoxide is sistance over many generations once much less than horse hemoglobin, but they have acquired it. Resistance seems it has a high aflfiinity for oxygen. Its to be inherited, but the method of functional significance, however, is genetic transmission is still in doubt. obscure. Colors of insects are as varied as The metabolism of chlorophyll, the those of the rainbow and arc frequently green pigment in plants, has been due to complex mixtures of pigments. studied in the silkworm, beetle, 34 Yearbook of Agriculture 1952 squash bug, and a few other species. that the molting process is controlled Many of the pigments in the squash by that are species-non- bug arc the results of the breakdown specific. Blood taken from an insect at of chlorophyll, the site of breakdown the proper time and injected into an apparently being the vcntriculus, or insect of another species will cause functional stomach. molting, although the injected insect Insects do not always produce their is not normally ready for the process. own pigments. Sometimes the colors The hormones, which have so many are the result of hereditary symbiotic varied functions, are secreted by at bacteria found in insect tissues. least 11 organs in insects. Physiological The wing pigments of the Pieridac, a functions which are -regu- common family of , were first lated are often influenced by tempera- studied by F. G. Hopkins in 1889. He ture and humidity or other environ- concluded that they were waste meta- mental factors. bolic products whose only physiolog- It has not been determined whether ical function is ornamental. The pig- hormones comparable to those ments mostly are now classified chem- found in the vertebrates are present in ically as pterincs. We have evidence insects. There are present in insects that they are not just ornamental. The physiologically active substances that pterine ring may be considered a de- participate in the development of he- rivative of riboflavin, which is usually reditary characters. Because of their present in the Malpighian tubes of in- similarity to hormones, they are called sects, for example. Thus there is a pos- gene hormones. sible connection with the metabolism Developmental hormones in the im- of vitamin Bo. The pterine ring is also mature stages are not always found in found in the folie acid molecule, which similar organs in all species, but they has been shown to be an essential me- are secreted by at least three , tabolite for the larva of the yellow- all located in the head of the insect: fever and the mealworm. The ; the ring gland, or The walkingstick Dixippus is dark- Weismann's ring; and some glandlikc colored at night and light-colored by cells of the . In adult insects, one day. Its color may be changed by illu- or more hormones secreted by the minating the insect at night or placing corpus allatum are important in repro- it in a dark place by day. The color of duction. Color changes are also appar- other species, such as the cabbage- ently due to the action of hormones. worm, Pieris hrassicae, is influenced by Some hormones cause metamorpho- the illumination of the larva as it rests sis. By the injection of material from before pupation. larvae ready to pupate, very young Hormones are chemical substances larvae have been made to undergo produced in an organ and liberated metamorphosis. But if a large larva is into the blood stream. Other organs divided into two sections by ligaturing then become excited by this hormone about 12 hours before time for normal and functional activity results. Much pupation, only the forward half will light has been shed on many phases of pupate, although the rear half will re- invertebrate endocrinology, which sci- main alive for many days. ence includes the hormones, since Ste- In the Cecropia silkworm, as in fan Kopec of Jagellonian University, many other insects, metamorphosis is Poland, in 1922, demonstrated the interrupted by a long period effect of a hormone on insect develop- that begins soon after the formation of ment. In insects, periods of great cell the . Diapause is characterized by activity are followed by a process called cessation of cellular growth. It appar- molting during which time the insect ently is caused by the destruction of sheds its old and is fitted with a enzymes involved in the cytochrome new and larger one. Kopec showed system. Following, the liberation of a Life Processes of Insects 35 growth hormone by cells in the pupal cuticle of flesh fly larvae ( Sarcophagi- brain and the stimulation by this hor- dae)^ 15^000 of these were found per mone of the prothoracic gland, the square millimeter. cytochrome system again begins to The cuticle cannot grow and, in the function and cell growth occurs. rigid parts of the insect, cannot be The outer covering of insects, the stretched. As the insect grows, there- integument, is both skeleton and skin. fore, the cuticle is shed and is replaced As in all arthropods, the integument by a larger cuticle. That process, molt- consists of an , one cell layer ing, follows a period of great cell activ- in thickness, and a hard cuticular mem- ity. When first laid down, the new cuti- brane. During their intermittent pe- cle is soft and often colorless, but it riods of activity, the epidermal cells rapidly hardens and assumes its normal secrete the circular membrane, com- color. monly called the cuticle, over the sur- The blow^ fly has been a favorite ex- face of the animal. Entomologists used perimental insect because its larval to believe that the characteristic com- cuticle is not shed before pupation, but ponent of cuticle was , a hard, rather is converted into the hard pupa- insoluble compound found in varying rium. In the flesh fly {Sarcophaga proportions in most insect . It harbata) the formation of the hard was thought that the chitin formed a puparium fromi the soft larval cuticle is framework in the interstices in which by the following process: Phenols are other components of the cuticle were oxidized enzymatically by polyphenol deposited. Scientists now believe that oxidase to orthoquinone. The ortho- proteins rather than chitin are the quinone combines with the protein fundamental constituents of cuticle. It present and hardens it by a tanning might be (as suggested by the interpre- process, during which the integument, tation of X-ray diffraction data) that which may have been colorless for a the cuticle consists of alternating layers short period after the molt, becomes of protein and chitin. colored brown or black. The colors due The cuticle may be rigid, flexible, or to tanning, however, are not the basis elastic. It also is waterproof; it has to for the brilliant iridescent or metallic be, because the integument keeps a colors of some insects. Such colors are proper water balance in the insect. The due usually to the interference in the epicuticlc, the thin outer membrane reflection of light from the multiple that is the most important in water- thin plates or scales that some insects proofing the cuticle, is a complex struc- have. ture of several layers. The first to be The shell, or chorion, of an insect's deposited is the innermost or cuticulin çigg is like cuticle in many ways, but is layer, believed to consist of a lipopro- even more complex. The shell of the tein, which perhaps is denatured, con- of the assassin bug, Rhodnius pro- densed, and finally tanned along with lixus, consists of seven layers, none of other proteins present in the outer lay- them waterproof. A cement layer is ers. Then a thick viscous fluid is dis- added to the outside of the egg when charged, and on top of that a wax it is laid. Waterproofing is effected by layer. The wax layer is then topped a thin w^ax layer on the inside of the with a hard cement layer, which is chorion, similar to the one that water- thought to consist of tanned proteins proofs the cuticle of most adult forms. combined with lipids. The cement The wax is secreted by the maturing layer is secreted by some of the dermal ç^gg and is attached securely to the glands whose openings are scattered innermost layer of the chorion. The over the surface of the integument. other layers are modifications of vari- Throughout the cuticle, running ver- ous proteinlike materials somewhat like tically from the cells, are the pore those in the cuticle. canals, of unknown function. In the The development of high-speed 36 Yearbook of Agriculture 1952 cameras^ with which many exposures tors of various species, although the per second are possible^ and cathode- actual organs are not always known. ray oscilloscopes, by which small In seeking materials that will attract changes in electrical potential can be and repel insects, research workers accurately recorded, has aided the have investigated the mechanical re- study of the physiology of . sponse of insects to thousands of com- When certain insects are held so that pounds that vaporize at body tempera- their feet arc in contact with a movable tures. Many of the compounds are syn- platform, the insect will rest quietly. thetic; many are natural materials of If the platform is removed, the insect unknown composition. moves its wings as in flight and many One such is a substance secreted by experiments can be done while the the female gypsy moth. It will attract insect is actually suspended in air male gypsy over long distances. under simulated flight conditions. If The method by which the worker small electrodes are inserted among honey bees inform other bees of the the flight muscles, potential changes location of a new food supply has been can be measured and correlated with described by , of the wing movement. Some butterflies move University of Munich. It has long been their wings at a leisurely 5 beats a sec- known that worker bees returning to ond, but certain midges attain about the hive often performed a kind of 1,000 wing beats a second. The vinegar dance on the comb, but the reason for fly is capable of flights lasting up to 2 the dance was obscure. Von Frisch hours. At the start, wing beats are found that by the direction and dura- about 300 per second but at the end, tion of their movements, during the when fatigue becomes evident, they dance, the worker bees transmitted to are about 100 a second. Among the other workers the direction and dis- insects with slow frequencies of wing tance from the hive to the new-found beats, the wing movements are com- food. He observed the antics in the pletely synchronous with nerve im- darkness of the hive by the use of red pulses, but when the frequency of wing light, to which the bees are insensitive. beat increases there is no synchrony. He found that he could predict the Insects, like the vertebrates, have distance to about 100 yards. Direction highly developed, specialized sensory was accurate to about 3°. The system receptors that can be stimulated by worked for any distance up to about chemicals. The chemical of in- 3.7 miles. For direction, the bees use sects may be roughly classified as taste, the sun as an orienting point. They smell, and the common chemical also are apparently sensitive to polar- of vertebrates whereby response is ized light, which they can use to get made to such irritants as ammonia and their bearings, because they can fly chlorine. The structure of the organs accurately whether or not the sun is of taste and smell of insects differ visible. greatly from that of the vertebrates, Dr. von Frisch's discoveries, like but a striking similarity exists in the others we have discussed, throw new physiological behavior toward many light into the mysteries of nature. More compounds and in the way in which such discoveries will come. They will stimulation is brought about. As among give us a better understanding of insect the vertebrates, however, the distinc- physiology, of better controls of insects, tion between taste and smell is based and, indeed, of all life processes, in- on unsatisfactory evidence. We cannot cluding our own. yet relegate either taste or smell in in- sects to specific areas of the body; areas FRANK H. BABERS^ a biochemist, is of contact have now in charge of a project that deals with been found on the mouth parts, tarsal the mode of action of insecticides and leg segments, antennae, and oviposi- physiology of insects. He is a grad- uate of the University of Florida and Princeton University. He joined the Department of Agriculture in iQS^- From ig46 to ig^S he was in charge How Insects Choose of the chemical section of the Orlando, Fla., laboratory of the Bureau of Ento- Their Food Plants mology and Plant Quarantine. JOHN J. PRATT, JR., joined the re- Charles T, Brues search staff of the Bureau of Ento- mology and Plant Quarantine upon receiving his doctor's degree from Cor- All forms of animal life need organic nell University in ig48. His work materials in order to exist, grow, and concerns the study of the mode of reproduce. Some subsist on living, action of insecticides, the development dead, or decaying plants. Others get of resistance to insecticides by insects, the they require from living or and insect physiology. dead . Suggested for further reference are Bee Many kinds, including some of the Venom Therapy; Bee Venom, Its Nature, insects, live on a mixed diet of both and Its Efifcct on Arthritic and Rheumatoid plant and animal materials. Civilized Conditions, hy Bodog F. Beck, D. Appleton- Century Co.,New York, /p^j; Physiologic de man has almost endless variety in his rinsects, hy Remy Chauvin, Institute Na-. diet: Bacteria, , fungi, roots, tional de la Recherchie Agronomique, Paris, berries, fruits, and foliage of plants 194g; Bees; Their Vision, Chemical Senses, furnish vegetable food ; he eats the flesh and Language, by Karl von Frisch, Cornell University Press, Ithaca, N. Y., 1950; Bib- of many invertebrate animals such as liography of Animal Venoms, by R. W. Har- and mollusks, although mon and C. B. Pollard, University of Florida , , and commonly Press, Gainesville, 1948; The Principles furnish his main protein requirements. of Insect Physiology, by V. B. Wigglesworth, Methuen and Company, London, 1950; and No insect selects food in such variety, the following articles in periodicals: but a few insects are omnivorous in the V. G. D et hier and L. E. Chadwick: sense that they may consume many kinds Chemoreception in Insects, Physiological of plant and animal materials. Most of Reviews, volume 28, pages 220-234. 1948. Hubert and Mabel Frings: The Loci of the more specialized kinds restrict their Contact Chcraoreceptors in Insects—a Re- diet to a limited range—particularly view With New Evidence, American Mid- the forms that develop as parasites land Naturalist, volume 41, pages 602-658. wdthin the bodies of host animals, which 1949- Aaron Bunsen Lerner and Thomas B. almost invariably are other insects. Fitzpatrick: Biochemistry of Melanin For- Such parasitic ones, which are called mation, Physiological Reviews, volume 50, entomophagous parasites, generally are pages 91-125. 1950. very specific in the selection of their William Träger: Insect Nutrition, Biolog- ical Reviews of the Cambridge Philosophical hosts. They usually lay their eggs on or Society, volume 22, pages 148-iyy. 1947. directly within the body of the host V. B. Wigglesworth: The Fate of Haemo- insect and continue from generation to globin in Rhodinius Prolixus (Hcmiptera) generation to confine their attacks to and Other Blood-Sucking Arthropods, Pro- the same species of hosts. ceedings of the Royal Society (London)^ series B, volume 131, pages S^S-SSQy I943> Predatory insects, which capture liv- and The Insect Cuticle, Biological Reviews ing prey just as do the carnivorous of the Cambridge Philosophical Society, vol- birds and mammals, confine their diet ume 23, pages 408-4.51. 1948. to animals smaller or less active than Carroll M. Williams: Biochemical Mech- anisms in Insect Growth and Metamorpho- themselves. Quite frequently they also sis, Federation Proceedings, volume 10, select particular kinds of prey: Some pages 546-552, 1950. consistently capture aphids, some de- J. Franklin Y eager: The Blood Picture of vour caterpillars, some feed on scale the Southern Armyworm (Prodenia Eri- dania), Journal of Agricultural Research, insects, and a few are addicted to a diet volume yi, pages 1-40, 1945- of snails. On the other hand, groups 37