Host odour alpha-pinene increases or reduces response of Ips avulsus (Coleoptera: Curculionidae: Scolytinae) to its aggregation pheromone, depending on separation of release points

Abstract

Abstract Monoterpenes in the resin of host trees are important host-location and -selection signals for conifer-infesting bark beetles and can increase or reduce responses to aggregation pheromones. Research on this interaction has been largely limited to collocated release points of the semiochemicals; however, sources are often separated in nature. I performed a trapping experiment to investigate whether distance between semiochemical release points influences how host monoterpene alpha-pinene affects Ips avulsus (Eichhoff) (Coleoptera: Curculionidae) response to its aggregation pheromone (ipsdienol and lanierone). High release (8 g/day) of alpha-pinene from a pheromone-baited trap caused a reduction in catches, but the same release of alpha-pinene from 4 m away significantly increased catches relative to pheromone alone. A low release (0.06 g/day) of alpha-pinene with either arrangement had no effect. Hence, a host odour released at rates sufficient to deter I. avulsus responses to its pheromone may nevertheless enhance attraction if the release point is sufficiently displaced from the pheromone source. The result suggests that, for I. avulsus, the semiochemical alpha-pinene may influence host finding and close-range assessment of host suitability in different ways. Operational lure formulations for some species of bark beetle might be improved by separating pheromone and host odour components or by adding a displaced host odour device.