Determination of the absolute configuration of female-produced contact sex pheromone components of the longhorned beetle, Neoclytus acuminatus acuminatus (F.) (Coleoptera: Cerambycidae)

Cuticular hydrocarbon components play important roles in short-range chemical communication in insects. Many of these cuticular compounds are methyl-branched hydrocarbons with one or more chiral centers, which can exist in two or more stereoisomeric forms. Although the importance of chirality for the volatile semiochemicals which insects use for long-range communication is well established, almost nothing is known about the role of chirality in insect contact chemoreception. In this study, we determined that the absolute configuration of the most abundant contact sex pheromone component, 7-methylpentacosane (7-MeC₂₅), of the cerambycid beetle Neoclytus acuminatus acuminatus (F.) is (R). The pheromone consists 7-MeC₂₅, 7-methylheptacosane (7-MeC₂₇) and 9-methylheptacosane (9-MeC₂₇). We then utilized enantiomerically pure synthetic pheromone components to test the hypothesis that males would respond more strongly to (R)- than to (S)-enantiomers of the three pheromone components. We also tested blends of (R)-7-MeC₂₅ with the (S)-enantiomers of the minor components and vice versa to determine if unnatural stereoisomers might inhibit mating behavior. Males responded most strongly to solvent-washed females treated with the blend of (R)-pheromone components, and responded to a lesser extent to the major component, (R)-7-MeC₂₇, alone. A blend of (R)-7-MeC₂₇ with the (S)-minor components elicited an intermediate response. Together, these findings suggest that the insects can discriminate the absolute configuration of the major and minor pheromone components, and that the configurations of all three components is likely to be (R).