INTERSPECIFIC ADVANTAGE RESULTS IN INTRASPECIFIC DISADVANTAGE - CHEMICAL PROTECTION VERSUS CANNIBALISM IN UTETHEISA ORNATRIX (LEPIDOPTERA, ARCTIIDAE)

This study suggests that alkaloid deficiency in Utetheisa (Lepidoptera : Arctiidae) is a main cause of cannibalism; moreover, cannibalism can be predicted on the basis of alkaloid deficiency and of systemic alka loid accumulation. This chemical plays a central role in the life of t his species, because, first, it provides acquired chemical protection from potential predators, and, second, it determines mating success (a s the alkaloid is an essential precursor of the male pheromone). Conse quently, losers in the larval sequestering of alkaloids, which would r esult in a lack of chemical protection and in decreased mating success , tend to target conspecific winners, which are normally substantially protected against a variety of predators; by cannibalizing those accu mulated alkaloid sources the losers tend to become the winners of cann ibalistic encounters while making up their shortfall of these chemical s. What is a presumptive advantage in selection under high predation p ressures and/or high alkaloid availabilities could become a disadvanta ge under high conspecific population densities and shortages of alkalo id supplies for larval uptake. Cannibalism may be expected to have gen eral ecological importance in the evolutionary play of Utetheisa and m ay contribute to a balanced regulation of the acquired alkaloid conten ts in these arctiid populations.