Postcopulatory sexual selection in an arctiid moth (Utetheisa ornatrix).

The offspring of twice-mated female Utetheisa ornatrix show low incidence of mixed paternity. Most progeny are sired exclusively by one male, the larger one, irrespective of parental age, male pyrrolizidine alkaloid content, mating order, between-mating interval, or duration of copulation. Data are presented suggesting that the female herself may exert control over the process by which one set of sperm is utilized at the expense of the other. Evidence for such postcopulatory female choice of sperm had not previously been obtained for an insect. Promiscuity provides the female with a means for accruing nuptial gifts (nutrients, defensive alkaloids). Sperm selection provides her with the option of utilizing sperm from larger, potentially more fit, males.