Attraction of Ips pini (Coleoptera: Scolytinae) and its predators to natural attractants and synthetic semiochemicals in northern California: Implications for population monitoring

Effective management of bark beetles (Coleoptera: Curculionidae, Scolytinae) relies on accurate assessments of pest and predator populations. Semiochemicals provide a powerful tool for attracting bark beetles and associated predators, but the extent to which trap catches reflect actual population densities are poorly understood. We conducted field experiments in California during 2 consecutive yr to determine how attraction of Ips pini (Say) and its major predators to synthetic pheromones vary from each other and from attraction to natural volatiles emitted from colonized hosts. Synthetic lures consisted of different ratios of the (+) and (-) enantiomers of ipsdienol, the primary pheromone component of I. pini, with or without lanierone, an additional component that synergizes attraction in some populations. I. pini was consistently attracted to either 3(+)/97(-) ipsdienol or infested host plant material. Lanierone had no effect on the attraction of I. pini. Coleopteran predators showed a range of responses, more of which coincided with I. pini. Temnochila chlorodia (Mannerheim) (Trogositidae) was attracted to infested host materials and all synthetic lures. Enoclerus lecontei (Wolcott) (Cleridae) preferentially responded to higher ratios of (+)-ipsdienol, and its attraction was strongly enhanced by lanierone. Enoclerus sphegeus F. was most attracted to infested hosts and exhibited a preference for (-)- over (+)-ipsdienol. Our results suggest that preferences of bark beetles and predators for bark beetle pheromones at the regional scale should be considered before deploying semiochemicals. These results are also consistent with a model of co-evolving responses to pheromones by predators and their prey. The roles of plant volatiles should be further investigated, both to improve monitoring programs and from an ecological perspective.