Mortality of coccinellid (Coleoptera : Coccinellidae) larvae and pupae when prey become scarce

Coccinellid larvae are known to prey upon conspecific and heterospecific eg gs, larvae, prepupae, and pupae. This behavior may depend on both the aggre gation and intensive search of potential cannibals and predators near aphid colonies and the disappearance of aphids before coccinellid larvae have co mpleted their development. We examined how coccinellid density and prey ava ilability influence cannibalism and interspecific predation of larvae and p upae of 4 species of coccinellids. We determined whether coccinellid mortal ity and dispersal were density-dependent when prey become scarce, and estim ated the leaving rates of Coleomegilla maculata (DeGeer), Adalia bipunctata (L.), and Hippodamia convergens (Guerin) larvae from plants with aphids an d plants without aphids. Our results show that larval and pupal cannibalism and interspecific predation occur more frequently when aphid populations c rash, but we found no evidence of coccinellid density-dependent mortality o r density-dependent larval dispersal among species. However, A. bipunctata and H. convergens were significantly more aggressive and more likely to lea ve a plant without aphids than was C. maculata. These results suggest that the decision to stay on a plant is not strongly aphid- or pollen-mediated f or C. maculata, but the decision to stay or leave does appear to be aphid-m ediated for H. convergens and to some extent A. bipunctata. Whether a cocci nellid larva stays or leaves and its tendency to cannibalize can affect lar val and pupal survival and the population dynamics of each species.