Recognition of an appropriate mating partner using cuticular hydrocarbons in a species with an extreme intra-sexual dimorphism

Attracting a mate at the right time is critical for many species that reproduce sexually. In insects, short-range communication between potential mates is often mediated by cuticular hydrocarbons (CHCs), which cover most of the insect cuticle. Although the CHC profiles of many insects have been studied, we know little about what aspects of a CHC profile cause changes in mate attractiveness over the lifetime of an individual. We addressed this question by studying the mason wasp Odynerus spinipes, whose females exhibit age-related quantitative changes in their CHC profile composition. First, we created an ethogram of the male mating behavior. We knew from preliminary investigations that males do not attempt to mate with recently eclosed adult females. By coating wasp dummies with different CHC extracts, we were able to show that the CHC profiles of 3-day-old females are indeed more attractive to males than those of 0-day-old females. The increased attractiveness of 3-day-old females compared to younger females was negatively correlated with the relative abundance of methyl-branched alkanes in the CHC profile of the females. These results, and the fact that the CHC profile of males is characterized by a high relative abundance of methyl-branched alkanes throughout the adult wasp lifetime, suggest that in O. spinipes, methyl-branched alkanes may act as anti-aphrodisiacs that reduce the harassment of females by males before the females are ready to mate.