Reproductive benefits derived from defensive plant alkaloid possession in an arctiid moth (Utetheisa ornatrix).

The moth Utetheisa ornatrix (family Arctiidae) depends on pyrrolizidine alkaloids (PAs) for defense. It sequesters the toxins as a larva from its food plants (Crotalaria species: family Fabaceae) and retains them through metamorphosis. We report here that PA-possession in the adult female U. ornatrix has a life-shortening effect, suggesting that, by putting the compounds to use, the moth may be incurring a cost. However, PA-possession also induces the female to oviposit at an accelerated rate, so that she does not, by dying earlier, incur a loss in fecundity. We argue that by "compressing" their adult existence into a shorter period, female U. ornatrix may actually accrue benefits.