The role of chemical communication in sexual selection: hair-pencil displays in the diamondback moth, Plutella xylostella

Theory suggests that if secondary sexual characteristics (or signals) are costly and females choose between mating partners, males should display more vigorously in the presence of competition. We investigated the use of chemical signals during courtship in the diamondback moth, Plutella xylostella. Males of P. xylostella have a hair-pencil gland on the tip of their abdomen, which allows for the release of chemical signals during courtship. Males detected potential competitors using chemical signals, but male investment in sexual signalling did not increase linearly in the presence of increasing numbers of competitors. The patterns of male display and mating behaviour among the parental population were not necessarily replicated among the next generation of males. Males of the parental generation that were exposed to one male competitor were more likely to display their hair-pencil than males exposed to zero or two competitors, but the display behaviour of the next generation of males (while higher overall) did not vary significantly across these treatments. Furthermore, males of the parental generation that acquired matings displayed their hair-pencil at a higher rate than males that did not obtain matings; again this pattern was not evident among the next generation of males. Finally, sons tended to be more likely to display their hair-pencil, and were significantly more likely to achieve a successful mating, than the previous generation of males. These intergenerational patterns suggest that the tendency to achieve copulations may have a genetic component.