Determination of the Absolute Configuration of Female-Produced Contact Sex Pheromone Components of the Longhorned Beetle, Neoclytus acuminatus acuminatus (F).

Cuticular hydrocarbons play important roles in contact chemical communication in insects. Many of these 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 that insects use for long-range communication is well established, almost nothing is known about the role of chirality in insect contact chemoreception. Here, we used reverse phase high performance liquid chromatography (RP-HPLC) and digital polarimetry to isolate and determine the absolute configuration of a component of the female-produced contact sex pheromone of the cerambycid beetle, Neoclytus acuminatus acuminatus (F.). The pheromone consists of 7-methylpentacosane (7-MeC25), 7-methylheptacosane (7-MeC27), and 9-methylheptacosane (9-MeC27). The absolute configuration of the most abundant pheromone component, 7-MeC25, was found to be (R). 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-MeC27, the most bioactive component, with the (S)-enantiomers of the minor components and vice versa to determine if unnatural stereoisomers might decrease behavioral responses. Males responded most strongly to solvent-washed females treated with the blend of (R)-pheromone components, and to a lesser extent to (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 configuration of all three components is likely to be (R).