Response Specificity of Dendroctonus terebrans (Coleoptera: Scolytidae) to Enantiomers of Its Sex Pheromones

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Abstract
The black turpentine beetle, Dendroctonus terebrans (Olivier), utilizes the bicyclic ketals frontalin, produced by females, and exo-brevicomin, produced by males, as sex pheromones. The isomer endo-brevicomin also is active behaviorally and may be produced by males, but its role is unclear. Responses of D. terebrans to traps baited with synthetic enantiomers of frontalin, exo-brevicomin, and endo-brevicomin were assayed in five field experiments. Males were strongly attracted to (â)-frontalin evaporated with pine turpentine (volatile host terpenes) and to racemic frontalin with turpentine, but (+)-frontalin was at best slightly attractive. Increased doses of (+)-frontalin did not interrupt the response of males to the (â) enantiomer. Both enantiomers of exo-brevicomin and the racemic solution were attractive to females when deployed with turpentine, as were (+), (â), and racemic endo-brevicomin. However, an experiment that examined the effect of exo-brevicomin on the response of males to turpentine and frontalin found that (+)-exo-brevicomin and the racemate were attractive to females, but the (â) enantiomer was not. Neither racemic exo-brevicomin nor either of the enantiomers interrupted the response of males to frontalin, unlike results from earlier studies that used high release rates of host volatiles. Although one enantiomer of both frontalin and exo-brevicomin was most active, their antipodes were not inhibitory and racemic material elicited responses similar to those elicited by the single enantiomers. Behavioral activity of (â)-frontalin and (+)-exo-brevicomin in D. terebrans is typical of the genus. In species of Dendroctonus for which enantiomeric specificity has been studied, (â)-frontalin and (+)-exo-brevicomin are behaviorally active and are produced in greater abundance compared with their respective antipodes.