V. G. Dethier.
Further Notes on Cannibalism Among Larvae.
Psyche 46:29-35, 1939.

Full text (searchable PDF, 608K)
Durable link: http://psyche.entclub.org/46/46-029.html

The following unprocessed text is extracted from the PDF file, and is likely to be both incomplete and full of errors. Please consult the PDF file for the complete article.

19391 Cannibalism Among Larvae
FURTHER NOTES ON CANNIBALISM AMONG
LARVAE
BY V. G. DETHIER
Biological Laboratories, Harvard University In a previous communication (Dethier, 1937) most of the reported cases of cannibalism among lepidopterous larvae were discussed. Hunger and crowding, with thirst as a contributing cause were found to be the prime factors in- ducing this anomalous diet. This confirms the conclusions of Hering (1926) whose book was previously unavailable to the writer. The present notes offer further explanatory data pertaining to hunger and crowding as causes of a meat diet. The effects of such a diet and the ability of a phyto- phagous larva to survive on one are considered. Additional cases are also cited.
I
In an effort to understand more fully the various causes initiating cannibalism and the carnivorous habit in general among lepidopterous larvas the following experiments were designed.
Two final instar larvae of Estigmene acrea Drury and one last instar larva of Isia isa:bella A. & S. were placed in a dry jar approximately twenty inches in volume. Also placed in the jar were one pupating E. acrea larva from which the cocoon had been removed, a smaller arctiid in similar con- dition, and one freshly killed /. Isabella larva which had been slit open longitudinally. The experimental animals had neither eaten nor drunk for four days. It was observed that they crawled ceaselessly around the bottom of the con- tainer exploring the surface with their antennae and mouth- parts. Some dry faeces when encountered were nibbled at slightly. No unusual behavior occurred until the slit carcass was encountered. Here the live animals immediately sucked up the body fluids. After a period of five minutes all three Psit-fte 4&29-15 (1939). hup Wpsycht einclub orgHW46-029 html



================================================================================

30 Psyche [March
experimentals were eating the tissues of the exposed larva. Next a decapitated Eneoptoloph~ sordidus Burm. was placed in the jar. Its metathoracic legs were removed to prevent kicking. The grasshopper was investigated by the larvae but no attack made upon it; however, when the carcaas was slit open, the larvse that chanced upon it started feeding almost immediately. The flesh, the eggs contained within the abdomen, and aa much of the cuticle as was not too heavily sclerotized were eaten. At this stage the small pupating arctiid was also eaten by the L Isabella. It can be seen from these observations that larvae are . more readily attacked and eaten when their tissues are exposed.
It is to be expected that caterpillars would be more attracted to exposed tissues because there is a more concentrated odor arising from them than from an insect completely sheathed in cuticle. Also, there is no stimulation of the mouthparts by an unmutilated carcass. On the other hand, body juices exposed to the air may stimulate the mouthparts directly. Further there is the possibility that tawse partaking of body juices are prompted to do so by thirst. An unmutilated carcass is attacked only when the larvse reach such a degree of starvation that they bite fre- quently at near-by objects.
In order to ascertain the exact series of events occurring when an animal with cannibalistic or carnivorous tendencies approaches another larva, a single live naked noctuid larva was placed in the jar with one E. uwea, In the limited area the two frequently encountered each other. The E. acres had reached the stage in which it bit at all objects encoun- tered. When it endeavored to take several bites of the noctuid, however, the latter thrashed about vigorously. Although the arctiid stabbed viciously at its intended victim several times, it finally withdrew. The noctuid's cuticle had not been pierced. On numerous occasions the same process was repeated. Finally the noctuid was rendered more or less quiescent by the buffeting of the more active and as- gressive arctiid. In this quiescent state, more or less bathed in its own regurgitated juices and those of its attacker, the noctuid was eaten. Undoubtedly this procedure takes place in most instances when one live insect is eaten by another. The higher percentage of cannibalism noted under crowded



================================================================================

19391 Cannibalism Among Larvae 31
conditions (Dethier, 1937) may be explained by the fact that chance meetings are more frequent. When similar conditions were reproduced in a cage twelve by sixteen inches, both animals eventually died of starvation. While experiments with mutilated animals indicate that thirst may be one factor in inducing cannibalism, the follow- ing experiments demonstrate that hunger by itself is an important factor.
One E. acrea was kept in a moist atmosphere, given its fill of water, and presented with every opportunity to continue drinking. When given a mutilated larva of the same species the experimental animal began feeding almost immediately. Repetitions of this experiment prove that hunger as distinct from thirst is one factor in inducing a carnivorous diet. The experimental animals never chose a diet of meat in preference to plants. Plant food was always accepted even after the larvae had gorged themselves with meat. In three hours a single E. acrea consumed one E. sordidus, another consumed one entire Gryllus assirnilis Fab., and an I. isabella consumed one full-grown larva of Vanessa virginiensis Drury. These three arctiids pupated and produced normal adults.
With regard, therefore, to the role played by hunger and crowding in causing cannibalism the following conclusions seem justified : First, the degree of hunger is of considerable importance. Larvae in the initial stages of hunger are not readily induced to eat flesh unless stimulated probably by the odor of the body fluids and more certainly by direct contact with them.
Larvae in the final stages of starvation yet still active enough to crawl about do not require such an intense stimulation. Since animals in this condition habitually nibble at near-by objects, they eventually bite through the integument of an intact carcass or a quiescent animal. At this juncture they too are stimulated by the flesh within. An exceedingly active victim is not actually eaten till it has been rendered more or less quiescent although it may still be capable of considerable movement. Second, crowding facilitates the initiation of the events already mentioned as caused by hunger. In addition crowding induces attacks not prompted by hunger (Balduf, 1931 ; Dethier, 1937). t




================================================================================

32 Psyche [March
It was observed that relatively large blocks of tissue were present in the faeces of these carnivorous larvae. In
order to facilitate the examination of these tissues to deter- mine what benefit the larvae were deriving from their diet the faeces were preserved in alcohol, sectioned in paraffin, and stained with Delafield's hematoxylin and eosin. Examination revealed that the tracheae as well as all other chitinous structures had passed through the alimen- tary canal completely untouched. This was to be expected since the occurrence of an enzyme acting upon chitin is very limited (Uvarov, 1928). Epithelium had been completely broken down. Relatively large blocks of muscle tissue were present in the faeces. These were recognizable as such; but digestion had been more or less complete, nothing remaining but a faint indication of the muscle fibers. No conclusion could be drawn concerning the fate of fat due to the histo- logical procedure employed. Plant material from the gut of the victim was also present in the faeces. Serial sections revealed that cell walls in the majority of cases were intact although the entire contents had been removed. This is in accord with Biedermann's (1919) contention that all the active components of the digestive juice can diffuse through cell membranes.
In order to throw further light upon the situation, larvae were tested for the presence of various digestive enzymes. Tests were adapted from Swingle's (1925), Wigglesworth's (l928), Cole's (l928), and Feigl's (1937) techniques. No attempt 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 reported from some species. Proteases and glycogenase also occur (Uvarov, 1928). It is apparent from the standpoint of the enzymes found present by various workers that phytopha- gous larvas are capable of digesting a meat diet. That both proteases and diastases occur in carnivorous insects and phytophagous insects alike is well known. As seen by the examination of faeces most of the con- stituents of a meat diet were utilized. Furthermore, all the



================================================================================

19391 Cannibalism Among Larvae 33
dietary requirements for complete development are met by a meat diet. The above considerations coupled with the fact that phytophagous larvae have been successfully raised to maturity on a meat diet refute the belief that a plant diet is necessary for the well-being of these larvae. The following additional reports of cannibalism and the carnivorous habit have been gleaned from the literature2 Most of them may be explained on the basis of the principles set forth above and in a previous paper. Riley, Packard, and Thomas (1883) stated that Laphygma frugiperda A. & S. and Cirphis unipuncta Haw. resort to cannibalism to satisfy their hunger when migrating. Many individuals are killed in this manner. Aitken and Davidson (1890) reported Ornithoptera minos Cram. as eating its own pupae when normal food was wanting. Witfield (1889) regarded Papilio ajax L. as showing more highly developed cannibalistic propensities than any other Papilionid larva of his acquaintance. Floersheim (1909) found, on the con- trary, that this species exhibits such behavior only during a shortage of food and then not very readily, since of twenty individuals but two were lost by cannibalism although the food shortage was extreme. Sorhagen (1899) listed all the cases (about eighty) of cannibalism known to him at the time. Forbes (1905) also reported L. frugiperda as being cannibalistic in nature when migrating. Thecla w-album according to Tutt (1905-1906) is commonly supposed to leave its food in order to feast upon the newly-formed pupae of its own species. Hering (1926) designated eighty-one speciesas 44Mordraupen'' of which nine cases had been re- ported as occurring in nature. This list is based on that of Sorhagen. Lommatzoch (1926) reported Spilosoma lubricipeda Esp. as eating a dead noctuid when its food supply had been exhausted. The report of Junglung (1930) that Scopelosoma satellitia L. resorted to coprophagy in captivity when food was lacking is interesting. Small larvse ^erg's paper quoted in Psyche 44(4): 114, 1937 was also reviewed in Kosmos, Zeit. f. einheitliche Weltanschauung auf Grund der Entwicklungslehre, 3 : 362-363, 1878.




================================================================================

34 Psyche [March
of Curpocapsa pornonella L, when crowded exhibit canni- balism (Balduf, 1931). Buckstone (1938) recorded an in- stance in which the larvaa of Pieris r w e L. and ova of P. brassicae were confined in the same box. When the latter emerged, they ate the former although the enclosed cabbage leaves 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 from correspondence with departmental officers in the field. During the summer of 1938 outbreaks of Cirphis mi- puneta Haw. occurred but no camibahsm was observed. However, Mr. R. P. Gorham reported that larvae under laboratory conditions fed on pup= although they showed no interest in larvae even when massed together in great num- bers. The same officer noticed no cannibalism in Nephelodes emmedmh Cram. Agrotis fewtica Tausch repeatedly at- tack one another in captivity. Mr. Gorham is of the opinion that most of our common garden cutworms are cannibalistic on pup= in the laboratory. No cannibalism was observed in Euxoa ochrogaster Gum. or Loxostege sticticdis L. Mr. K. M. King and Mr. H. L. Seamans report that larger lawee of Agrotis orthogonia Morr. attack smaller and weaker ones especially in the laboratory. Chizagrotis auxilmris Grote according to Mr. Seamans is markedly cannibalistic under conditions of migration. When the advance of the larvae is checked by some obstacle such as a furrow, the weaker larvae are quickly attacked. Curiously enough larvae which have been killed by poisoned bait are frequently eaten. Aitken, E, H. and Davidson, J., 1890. Notes on the larvae and pupae of some of the butterflies of the Bombay Presidency. J. Bombay
Nat. Hist. Soc., 5:362.
Balduf, W. V,, 1931. Carnivorous moths and butterflies. Trans. Illinois State Acad. Sci., 24(2) : 166-164. 1938. The rise of entotaophagy among Lepidoptera. American Nat., 72: 358-379.
Biedermann, W., 1911. Die Aufnahme, Verftrbeitung und Assimilation der Nahrung. Pt. 9. Die Erniihrung der Insekten. Winter- stein, Handb. vergl. Physiol. 2(1) : 726-902. -1919. Beitrage zur vergleichenden Physiologic VII and VIIL Pflugers Archiv f, die ges. Physiologic, 174: 358-425,



================================================================================

Cannibalism Among Larvae
Buckstone, 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 larvas. Psyche, 44(4) : 110-115.
Dirks, E., 1922. Liefern die Malpighischen Gefasse Verdauungsekrete? Arch. f. Natura-esch.. 4: 161-220.
Feigl, F., 1937. ~uagtative Analysis by Spot Tests, 314-316, N. Y. Floersheim, C., 1909. Larval habits of Iphiclides ajax. Ent. Rec., 21 (5) : 113-115.
Forbes, S. A., 1905. 23d Report State Ent. Illinois, 82. Hering, M., 1926. Biologie der Schmetterlinge, 71-75, Berlin. Junglung, G., 1930. Ein Fall von Koprophagie (Kotfressen) bei Scopelosoma satellitia L. (Lep.). Ent. Zeit. Frankfurt a. M., 43: 57.
Lommatzoch, W., 1926. Sonderbare Mordegeluste einer Raupe. Int. Ent. Zeit., 20: 232.
Riley, C. V., Packard, A. S., and Thomas, C., 1883. Third Report of the U. S. Ent. Commission, 117.
Sorhagen, L., 1899. Mordraupen. Illustr. Zeit. f. Ent., 4(4): 49-51, 4(6) : 82-85, 4(9) : 135-137.
Straus, J., 1909. Uber das Vorkommen einiger Kohlenhydratfermente bei Lepidopteren und Dipteren in verschiedenen Entwicklungs- stadien. Zeit. f. Biol., 52 (1-3) : 95-106. 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 of t'he literature. Trans. London Ent. Soc., 76(2) : 255-343. " Wigglesworth, V. B., 1928. Digestion in the cockroach. I11 The diges- tion of proteins and fats. Biochem. J., 22(1) : 150-161. Witfield, 1889. Scudder's Butterflies of the Eastern United States and Canada, 2: 1273.




================================================================================