Mate location strategies of gypsy moths in dense populations.

In high-density populations, the male gypsy moth (Lymantria dispar) "appetitive" flight is primarily vertical and within 1-50 cm of tree boles. Preceding location of a female, males land on trees or occasionally tree foliage and walk while wing-fanning. In high-density populations females may mate before calling, often prior to wing expansion or hardening. Additional matings may occur before any or full deposition of egg masses. Virgin females are not coy, whether their wings are unexpanded, or hardened and held rooflike, or whether they are calling or not. They generally mate with the first willing male and do not exercise sexual selection by an acceptance or rejection reaction. The mating structure in dense populations would seem to reduce selective pressure for female emission of and direct male anemotactic flight to attractant pheromone. A low proportion of males "search" appropriate objects, especially tree trunks, in the walking-wing-fanning state. Such males often are successful in locating virgin females before calling commences. This male strategy presumably would not be successful in low population densities.