Interspecific advantage results in intraspecific disadvantage: Chemical protection versus cannibalism inUtetheisa ornatrix (Lepidoptera: Arctiidae).

This study suggests that alkaloid deficiency inUtetheisa (Lepidoptera: Arctiidae) is a main cause of cannibalism; moreover, cannibalism can be predicted on the basis of alkaloid deficiency and of systemic alkaloid accumulation. This chemical plays a central role in the life of this species, because, first, it provides acquired chemical protection from potential predators, and, second, it determines mating success (as the alkaloid is an essential precursor of the male pheromone). Consequently, losers in the larval sequestering of alkaloids, which would result 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 accumulated alkaloid sources the losers tend to become the winners of cannibalistic encounters while making up their shortfall of these chemicals. What is a presumptive advantage in selection under high predation pressures and/or high alkaloid availabilities could become a disadvantage under high conspecific population densities and shortages of alkaloid supplies for larval uptake. Cannibalism may be expected to have general ecological importance in the evolutionary play ofUtetheisa and may contribute to a balanced regulation of the acquired alkaloid contents in these arctiid populations.