(Z)-9-Nonacosene—Major Component of the Contact Sex Pheromone of the Beetle Megacyllene caryae

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Abstract
Male Megacyllene caryae (Gahan) (Coleoptera: Cerambycidae) respond to females only after touching them with their antennae, indicating that mate recognition is mediated by a contact sex pheromone. Gas chromatography-mass spectrometry analyses of whole-body solvent extracts of male and female M. caryae revealed substantial differences in hydrocarbon profiles, with nearly half of the compounds in the extracts from females being absent from those of males. Biological activities of fractions of crude extracts of females, and reconstructed blends of the most abundant straight-chain (nC27, nC28, nC29), methyl-branched (2Me-C26, 9Me-C29, 11, 13, 15Me-C29), and unsaturated (Z9:C29, Z13:C29, Z14:C29, Z13:C31, Z14:C31, Z15:C31) compounds in extracts of females were tested in arena bioassays, assessing four steps in the mating behavior sequence of males (orientation, arrestment, body alignment, mounting and attempting to couple the genitalia). Males showed limited response to dead females treated with fractions of the crude extract or blends of synthetic straight-chain and methyl-branched alkanes, but responded strongly to the blend of synthetic monoenes. Further trials determined that the complete sequence of mating behaviors, up to and including coupling the genitalia, was elicited by Z9:C29 alone. Z9:C29 is a homolog of the contact pheromone (Z9:C25) of the congener M. robiniae (Förster). Previous work with M. robiniae suggested that wipe sampling of cuticular hydrocarbons of females by solid phase microextraction yielded a more representative profile of components actually encountered by a male’s antennae, and so provided a more readily interpretable profile of potential semiochemicals present in the wax layer than does solvent extraction. We tested this hypothesis by comparing hydrocarbon profiles of female M. caryae by the two sampling methods. Z9:C29 was the only compound among the dominant hydrocarbons that was present in higher abundance in SPME than in solvent extracts (∼12% vs. ∼8%, respectively), supporting this hypothesis.

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