Enantiospecific responses of southern pine beetle (Dendroctonus frontalis) and its clerid predator, Thanasimus dubius, to a-pinene.
Multi-trophic interactions between pine bark beetles, their host trees, and predators are mediated in part by volatile terpenes in host tree oleoresin that can influence aggregation and/or host finding by both prey and predator species. The southern pine beetle, Dendroctonus frontalis Zimmermann, mass-attacks pine trees in response to its aggregation pheromone combined with host resin odors including a-pinene. We investigated discrimination of apinene enantiomers in olfactory responses of D. frontalis, and in behavioral responses of D. frontalis and its major clerid predator, Thanasimus dubius (Fabricius). Trapping trials in the spring and fall assessed attraction of both species to the D. frontalis aggregation pheromone components, frontalin and endo-brevicomin, either alone or in combination with a-pinene lures of differing enantiomeric compositions. a-Pinene lures enriched with the (?)-enantiomer (97.5 %) increased D. frontalis catches significantly more than (-)-enriched (93 %) lures, but did not differ from racemic lures. Sexes of D. frontalis did not differ from one another in their responses to the enantiomers, and there was no difference in lure discrimination by D. frontalis and T. dubius. Thanasimus dubius did not distinguish between different a-pinene enantiomers. Dose–response electroantennogram studies of D. frontalis indicated that their antennae had a slightly lower response threshold to (?) than (-)-a-pinene. Each enantiomer habituated the antennae more to itself than to its antipode, implying the existence of olfactory receptors with differing affinities for enantiomers. The preference of D. frontalis for (?)-apinene may affect its host selection behavior, and should be considered in population monitoring lures.