Chemical basis of egg cannibalism in a caterpillar (Utetheisa ornatrix).

Larvae of the mothUtetheisa ornatrix are shown to cannibalize eggs in the laboratory. They proved most cannibalistic if they were systemically deficient in pyrrolizidine alkaloid (PA), the defensive agent that protectsUtetheisa at all stages of development against predation, and whichUtetheisa acquire as larvae from their food plant. In exercising cannibalistic choice,Utetheisa larvae feed preferentially on eggs that are PA-Iaden rather than PA-free. Egg cannibalism can therefore provideUtetheisa with a supplemental means of PA procurement. Moreover, presence of PA in the egg, while providing the egg with defense against predation, can increase its vulnerability to cannibalism. Although evidence is presented thatUtetheisa larvae cannibalize eggs in nature, it is argued that such feeding may occur only opportunistically in the wild, rather than as a matter of course.