V. G. Dethier

Psyche : A Journal of Entomology

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19391 Cannibalism Among Larvae 29FURTHER NOTES ON CANNIBALISM AMONGLARVAEBY V. G. DETHIERBiological Laboratories, Harvard UniversityIn a previous communication (Dethier, 1937) most of thereported cases of cannibalism among lepidopterous larvmwere discussed. Hunger and crowding, with thirst as acontributing cause were found to be the prime factors in-ducing this anomalous diet. This confirms the conclusionsof Hering (1926) whose book was previously unavailable tothe writer. The present notes offer further explanatorydata pertaining to hunger and crowding as causes of a meatdiet. The effects of such a diet and the ability of a phyto-phagous larva to survive on one are considered. Additionalcases are also cited.IIn an effort to understand more ully the various causesinitiating cannibalism and the carnivorous habit in generalamong lepidopterous larvm the ollowing experiments weredesigned.Two final instar larvm of Estigmene a.crea Drury and onelast instar larva o Isia isabella A. & S. were placed in adry jar approximately t.wenty inches in volume. Also placedin the jar were one pupating E. acrea larva rom which thecocoon had been removed, a smaller arctiid in similar con-dition, and one reshly killed I. isa,bella larva which hadbeen slit open longitudinally. The experimental animals hadneither eaten nor drunk ior our days. It was observedthat they crawled ceaselessly around the bottom o2 the con-tainer exploring the surface with their antennm and mouth-parts. Some dry 2races when encountered were nibbled atslightly. No unusual behavior occurred until the slit carcasswas encountered. Here the live animals immediately suckedup the body fluids. After a period of five minutes all three30 Psyche [Marchexperimentals were eating the tissues oi the exposed larva.Next a decapitated Encoptolophus sordidus Burm. wasplaced in the jar. Its metathoracic legs were removed toprevent kicking. The grasshopper was investigated by thelarvm but no attack made upon it; however, when the carcasswas slit open, the larvm that chanced upon it started feedingalmost immediately. The flesh, the eggs contained withinthe abdomen, and as much of the cuticle as was not tooheavily sclerotized were eaten. At this stage the smallpupating arctiid was also eaten by the I. isabella.It can be seen from these observations that larvae aremore readily attacked and eaten when their tissues areexposed. It is to be expected that caterpillars would bemore attracted to exposed tissues because there is a moreconcentrated odor arising rom them than rom an insectcompletely sheathed in cuticle. Also, there is no stimulationof the mouthparts by an unmutilated carcass. On the otherhand, body juices exposed to the air may stimulate themouthparts directly. Further there is the possibility thatlarvm partaking o2 body juices are prompted to do so bythirst. An unmutilated carcass is attacked only when thelarvm reach such a degree of starvation that they bite re-quently at near-by objects.In order to ascertain the exact series of events occurringwhen an animal with cannibalistic or carnivorous tendenciesapproaches another larva, a single live naked noctuid larvawas placed in the jar with one E. acrea. In the limited areathe two requently encountered each other. The E. a.creahad reached the stage in which it bit at all objects encoun-tered. When it endeavored to take several bites o thenoctuid, however, the latter thrashed about vigorously.Although the arctiid stabbed vici,ously at its intended victimseveral times, it finally withdrew. The noctuid’s cuticle hadnot been pierced. On numerous occasions the same processwas repeated. Finally the noctuid was rendered more orless quiescent by the buff.eting of the more active and ag-gressive arctiid. In this quiescent state, more or less bathedin its own regurgitated juices and those of its attacker, thenoctuid was eaten. Undoubtedly this procedure takes placein most instances when one live insect is eaten by another.The higher percentage of cannibalism noted under crowded1939] Cannibalism Among Larvae 31conditions (Dethier, 1937) may be explained by the actthat chance meetings are more requent. When similarconditions were reproduced in a cage welve by sixteeninches, both animals eventually died oi starvation.While experiments with mutilated animals indicate thatthirst may be one actor in inducing cannibalism, the ollow-ing experiments demonstrate that hunger by itsel is animportant 2actor.One E. acrea was kept in a moist atmosphere, given its fillo water, and presented with every opportunity to continuedrinking. When given a mutilated larva o2 the same speciesthe experimental animal began eeding almost immediately.Repetitions o this experiment prove that hunger as distinctrom thirst is one actor in inducing a carnivorous diet.The experimental animals never chose a diet o meat inpreference to plants. Plant food was always accepted evenafter the larwe had gorged themselves with meat. In threehours a single E. acrea consumed one E. s.ordidus, anotherconsumed one entire Gryllus assimilis Fab., and an I. isabellaconsumed one ull-grown larva of Vanessa virginiensisDrury. These three arctiids pupated and produced normaladults.With regard, therefore, to the r61e played by hunger andcrowding in causing cannibalism he ollowing conclusionsseem justified- First, the degree o hunger is of considerableimportance. Larvae in the initial stages o.f hunger are notreadily induced to eat flesh unless stimulated probably by theodor o2 the body fluids and more certainly by direct contactwith them. Larvae in the final stages o starvation yet stillactive enough to crawl about do not require such an intensestimulation. Since animals in this condition habituallynibble at near-by objects, they eventually bite through theintegument of an intact carcass or a quiescent animal. Atthis juncture they too are stimulated by the flesh within.An exceedingly active victim is not actually eaten till it hasbeen rendered more or less quiescent although it may stillbe capable o considerable movement. Second, crowding2acilitates the initiation o the events already mentioned ascaused by hunger. In addition crowding induces attacksnot prompted by hunger (Baldu, 1931; Dethier, 1937).32 Psyche [MarchIIIt was observed that relatively large blocks of issuewere present in the i’eces of these carnivorous larvae. Inorder to facilitate the examination of these tissues to deter-mine what benefit the larvae were deriving from their dietthe faces were preserved in alcohol, sectioned in paraffin,and stained with Delafield’s hematoxylin and eosin.Examination revealed that the tracheae as well as allother chitinous structures had passed through the alimen-tary canal completely untouched. This was to be expectedsince the occurrence of an enzyme acting upon chitin is verylimited (Uvarov, 1928). Epithelium had been completelybroken down. Relatively large blocks of muscle issue werepresent in the feces. These were recognizable as such; butdigestion had been more or less complete, nothing remainingbut a faint indication of the muscle fibers. No conclusioncould be drawn concerning the fate of fat due to the histo-logical procedure employed. Plant material from the gut ofthe victim was also present in the feces. Serial sectionsrevealed that cell walls in the majority of cases were intactalthough the entire contents had been removed. This is inaccord with Biedermann’s (1919) contention that all heactive components of the digestive juice can diffuse throughcell membranes.In order to throw further light upon the situation, larvaewere tested for the presence of various digestive .enzymes.Tests were adapted from Swingle’s (1925), Wigglesworth’s(1928), Cole’s (1928), and Feigl’s (1937) techniques. Noattempt was made to conduct a differential analysis. In-vertase and maltase were present. Neither lipase, lactase,nor amylase were detected. Amylase had been found occur-ring quite commonly, however (Dirks, 1922; Straus, 1909;Biedermann, 1911 and 1919). Lactase had been reportedfrom some species. Proteases and glycogenase also occur(Uvarov, 1928). It is apparent from the standpoint of heenzymes found present by various workers that phytopha-gous larvae are capable of digesting a meat diet. Tha bothproteases and diastases occur in carnivorous insects andphytophagous insects alike is well known.As seen by he examination of feces most of the con-stituents of a meat diet were utilized. Furthermore, all the1939] Cannibalism Among Larvae 33dietary requirements 2or complete development are met bya meat diet. The above considerations coupled with the actthat phytophagous larvm have been successfully raised tomaturity on a meat diet refute the belie2 that a plant diet isnecessary or the well-being of these larvm.IIIThe following additional reports of cannibalism and thecarnivorous habit have been gleaned from the literature.Most of them may be explained on the basis of the principlesset forth above and in a previous paper.Riley, Packard, and Thomas (1883) stated that Laphygmafrugiperda A. & S. and Cirphis unipuncta Haw. resort tocannibalism to satisfy their hunger when migrating. Manyindividuals are killed in this manner. Aitken and Davidson(1890) reported Ornitho.ptera minos Cram. as eating itsown pupm when normal food was wanting. Witfield (1889)regarded Papilio ajax L. as showing more highly developedcannibalistic propensities than any other Papilionid larvaof his acquaintance. Floersheim (1909) found, on the con-trary, that this species exhibits such behavior only during ashortage of food and then not very readily, since of twentyindividuals but two were lost by cannibalism although thefood shortage was extreme. Srhagen (1899) listed all thecases (about eighty) ofcannibalism known to him at thetime. Forbes (1905) also reported L. frugiperda as beingcannibalistic in nature when migrating. Thecla w-albumaccording to Tutt (1905-1906) is commonly supposed toleave its food in order to feast upon the newly-formed pupmo its own species. Hering (1926) designated eighty-onespecies,.as "Mordraupen" of which nine cases had been re-ported as occurring in nature. This list is based on thatof Sorhagen. Lommatzoch (1926) reported Spilosomalu,bricipeda Esp. as eating a dead noctuid when its oodsupply had been exhausted. The report of Junglung (1930)that Scopelosoma satellitia L. resorted to coprophagy incaptivity when ood was lacking is interesting. Small larvm1Berg’s paper quoted in Psyche 44(4): 114, 1937 was also reviewedin Kosmos, Zeit. f. einheitliche Weltanschauung auf Grund derEntwicklungslehre, 3: 362-363, 1878.34 Psyche [MarchOf Carpocapsa pomonella L. when crowded exhibit canni-balism (Balduf, 1931). Buckstone (1938) recorded an in-stance in which the larvm of Pieris rapae L. and ova ofP. brassicae were confined in the same box. When the latteremerged, they ate the former although the enclosed cabbageleaves were still fresh.With further regard to cannibalism under natural con-ditions I am grateful to Dr. H. G. Crawford of the Depart-ment of Agriculture, Canada for permission to quote romcorrespondence with departmental officers in the field.During the summer of 1938 outbreaks of Cirphis uni-puncta Haw. occurred but no cannibalism was observed.However, Mr. R. P. Gorham reported that larvm underlaboratory conditions fed on pupm although they showed nointerest in larvm even when massed together in great num-bers. The same officer noticed no cannibalism in Nephelodesemmedonia Cram. Agrotis fennica Tausch repeatedly at-tack one another in captivity. Mr. Gorham is of the opinionthat most of our common garden cutworms are cannibalisticon pupa in the laboratory. No cannibalism was observed inEuxoa ochrogaster Guen. or Loxostege sticticalis L. Mr.K. M. King and Mr. H. L. Seamans report that larger larvaeof Agrotis orthogonia Morr. attack smaller and weaker onesespecially in the laboratory. Chizagrotis auxiliaris Groteaccording to Mr. Seamans is markedly cannibalistic underconditions of migration. When the advance of the larvm ischecked by some obstacle such as a furrow, the weakerlarvm are quickly attacked. Curiously enough larvm whichhave been killed by poisoned bait are frequently eaten.LITERATURE CITEDAitken, E. H. and Davidson, J., 1890. Notes on the larvae and pupmof some of the butterflies of the Bombay Presidency. J. BombayNat. Hist. Soc., 5:362.Balduf, W. V., 1931. Carnivorous moths and butterflies. Trans.Illinois State Acad. Sci., 24(2): 156-164.1938. The rise of entomophagy among Lepidoptera. AmericanNat., 72: 358-379.Biedermann, W., 1911. Die Aufnahme, Verarbeitung und Assimilationder Nahrung. Pt. 9. Die Ernihrung der Insekten. Winter-stein, Handb. vergl. Physiol. 2(1): 726-90.2.1919. Beitrige zur vergleichenden Physiologie VII and VIII.Pfliigers Archiv f. die ges. Physiologie, 174" 358-425.1939] Cannibalism Among Larvae 35Buckstone, A. A. W., 1938. Pieris rap a cannibal. Entomologist,71 (897) 34.Cole, S. W., 1928. Practical Physiological Chemistry. 8th ed.,Baltimore.Dethier, V. G., 1937. Cannibalism among lepidopterous larvae.Psyche, 44(4) 110-115.Dirks, E., 1922. Liefern die Malpighischen Gefisse Verdauungsekrete ?Arch. 2. Naturgesch., 4: 161-220.Feigl, F., 1937. Qualitative Analysis by Spot Tests, 314-316, N. Y.Floersheim, C., 1909. Larval habits o2 Iphicldes. ajax. Ent. Rec.,21(5) 113-115.Forbes, S. A., 190.5. 23d Report State Ent. Illinois, 82.Hering, M., 1926. Biologie der Schmetterlinge, 71-75, Berlin.Junglung, G., 1930. Ein Fall von Koprophagie (Kotfressen) beiScopelosoma satellitia L. (Lep.). Ent. Zeit. Frankfurt. a. M.,43: 57.Lommatzoch, W., 1926. Sonderbare Mordegeltiste einer Raupe. Int.Ent. Zeit., 20" 232.Riley, C. V., Packard, A. S., and Thomas, C., 1883. Third Report o2the U. S. Ent. Commission, 117.Sorhagen, L., 1899. Mordraupen. Illustr. Zeit. . Ent., 4.(4): 49-51,4(6): 82-85, 4(9) 135-137.Straus, J., 1909. tber das Vorkommen einiger Kohlenhydratfermentebei Lepidopteren und Dipteren in verschiedenen Entwicklungs-stadien. Zeit. . Biol., 52(1-3): 95-10’6.Swingle, H. S., 1925. Digestive enzymes of an insect. Ohio J. Sci.,25 (5) 209-218.Tutt, J. W., 1905-1906. British Lepidoptera, 8" 37, London.Uvarov, B. P., 1928. Insect nutrition and metabolism. A summary ofthe literature. Trans. London Ent. Soc., 76(2): 255-343.Wigglesworth, V. B., 1928. Digestion in the cockroach. III The diges-tion of proteins and fats. Biochem. J., 22(1): 150-161.Witfield, 1889. 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Further Notes on Cannibalism Among Larvæ

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Further Notes on Cannibalism Among Larvæ

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