The role of cuticular hydrocarbons in male mating behavior of the mustard leaf beetle, Phaedon cochleariae (F.).

We investigated the role that cuticular hydrocarbons (CHC) play in sexual communication by the mustard leaf beetle, Phaedon cochleariae (Coleoptera: Chrysomelidae). In laboratory bioassays, male P. cochleariae attempted to copulate with living or freeze-killed females as often as with males. However, the duration of copulation with females was longer than with males. To elucidate the impact of CHC on this behavior, cuticular compounds of adults of both sexes were extracted with dichloromethane. Male mating attempts with glass beads treated with the dichloromethane extract were nearly as frequent as with living beetles. The dichloromethane extract was fractionated by silica gel chromatography, and the biological activity of the fractions was tested by applying them to glass beads. A non-polar hexane fraction significantly elicited mating behavior, whereas the polar methanol fraction did not, likely because it contained defensive compounds from exocrine glands located in the elytra and pronota. Interestingly, a mixture of both the non-polar and polar fraction tended to elicit more mating attempts than did the non-polar hexane fraction alone. Further fractionation of the significantly active hexane fraction by silver nitrate column chromatography revealed that saturated CHC elicited mating behavior, but the olefins did not. GC-MS analyses of dichloromethane cuticular extracts showed that the male and female CHC profiles were qualitatively identical, but differed in their relative composition. Canonical discriminant analysis showed that CHC profiles of males and females formed separate clusters. Nevertheless, the results of our bioassays demonstrated that male and female CHC did not elicit sex discriminative male behavior, but induced mating by males regardless of the sex of the partner.