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Some Developmental Consequences of Handling, Egg‐eating, and Population Density for Flour Beetle Larvae

Mertz, David B., Robertson, J. Roy
Ecology 1970 v.51 no.6 pp. 989-998
Tribolium castaneum, brewers yeast, cannibalism, climate, eggs, insect larvae, mortality, natural selection, population density, pupation, rearing, social parasitism, whole wheat flour
Unhandled larvae of Tribolium castaneum (genetic strain cIV—a) were reared in a whole—wheat flour medium (Fortified with dried powdered brewer's yeast, 5% by weight) in a climate of 29°C and 70% RH at three levels of crowding: 100, 200, and 400 per 8 g of flour. At all three densities the median time for pupation was about 18.15 days. Mortality of the developing stages was 3—4% at the 2 lowest densities and about 8% for 400 larvae. Larvae which were subjected to daily handling and reared at the same densities developed more slowly, the prolongation of the larval stage being greatest at density 400. Handling also induced increased mortality at this density but not at lower densities. Handled larvae which were fed eggs of their own kind grew more rapidly than those not fed eggs, and, at the highest egg—feeding rates, the effects of handling and density were almost completely compensated. Evidence is presented that egg—eating would also accelerate the development of unhandled larvae. This is one of the most convincing demonstrations of a nutritional gain on the part of Tribolium cannibals as opposed to noncannibals. We suggest that cannibalism, which is capable of regulating Tribolium populations, is a form of social parasitism which may be favored by natural selection.