Does the Stereochemistry of Methylated Cuticular Hydrocarbons Contribute to Mate Recognition in the Egg Parasitoid Wasp Ooencyrtus kuvanae?

Close-range sexual communication of the egg parasitoid wasp Ooencyrtus kuvanae (Hymenoptera: Encyrtidae) takes place on host gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae), egg masses. We tested the hypothesis that mate recognition in O. kuvanae is mediated, in part, by low-volatility cuticular hydrocarbon (CHC) pheromone components. Gas chromatographic and GC-mass spectrometric analyses of body surface extracts of male and female wasps revealed no sex-specific components, but 5-methylheptacosane (5-me-27Hy) and 5,17-dimethylheptacosane (5,17-dime-27Hy) were consistently more abundant in extracts of males. The ratio of 5-me-27Hy and 5,17-dime-27Hy was similar in extracts of males and females, and quantitative differences alone seemed insufficient to impart sex-specific CHC profiles. Therefore, we further hypothesized that the absolute configuration of 5-me-27Hy and 5,17-dime-27Hy contributes to mate recognition or attraction. As the stereoisomers of 5-me-27Hy and 5,17-dime-27Hy cannot currently be separated chromatographically, we could not determine the stereochemistry of the insect-produced components. Instead, we synthesized all stereoisomers and bioassayed synthetic blends in laboratory experiments. Of eight 2-component blends, each blend containing one of the two enantiomers of 5-me-27Hy and one of the four stereoisomers of 5,17-dime-27Hy, the blend of (5 S )-methylheptacosane and (5 R ,17 S )-dimethylheptacosane attracted males, whereas the blend of (5 R )-methylheptacosane and (5 R ,17 R )-dimethylheptacosane repelled males. Apparent recognition of both pheromone components and pheromone antagonists by males supports the hypothesis that the stereochemistry of 5-me-27Hy and 5,17-dime-27Hy, and possibly other methylated CHCs, may differ between male and female O. kuvanae, and that these differences may serve in mate attraction and recognition.