Host compounds as kairomones for the western balsam bark beetle Dryocoetes confusus Sw. (Col., Scolytidae)

Six compounds attractive to the western balsam bark beetle Dryocoetes confusus in laboratory bioassays were isolated by micropreparative gas chromatography from steam distilled phloem oil from subalpine fir, Abies lasiocarpa (Hook.) Nutt. In the bioassays (1S)-(-)-α-pinene, p-cymene, terpinolene, (+)-longifolene, (R)-(-)-myrtenal and transpinocarveol were attractive at 1 μg doses to both sexes of beetles. When combined with 10 pg doses of (±)-exobrevicomin, all except terpinolene increased the responses to exo-brevicomin in an additive manner. In field experiments in British Columbia, none of the isolated compounds alone was attractive to D. confusus in multiple funnel traps. When paired singly or together with a 9:1 blend of (+)-exo- and (+)-endo-brevicomin released at 0.2 mg per day, (1S)-(-)-α-pinene and (R)-(-)-myrtenal released at 12 and 2 mg per day, respectively, caused a significant increase in response by male beetles over the response to the 9:1 blend alone. Myrtenal also increased the response of females. Because iris inexpensive and stable, (1S)-(-)-α-pinene could be used to improve the sensitivity of pheromone-baited traps for monitoring D. confusus. However the pheromone blend alone is a highly efficacious tree bait, and host tree kairomones would probably not be needed in baits used to manipulate D. confusus infestations.