Cannibalism, optimal egg size and vulnerable developmental stages in insect predators

Cannibalism in insect predators is widely reported and commented on. However, the reasons for the high levels of cannibalism observed, the vulnerability of certain developmental stages, and its adaptive significance are poorly understood. Here we show that unlike in parasitoids there could be advantages for a predator in laying many small eggs, rather than fewer large eggs. The temporal incidence of cannibalism within a patch is possibly a consequence of changes in the ratio of predator to prey numbers and/or changes in the vulnerability of the developmental stages of the predator. Cannibalism is advantageous for cannibals because conspecifics are a rich source of food for larval development or egg production, and it reduces intraspecific competition. Adults reduce the cannibalism of their offspring by not ovipositing in patches of prey where conspecific larvae are present.