Attraction of Ips pini (Coleoptera: Scolytidae) and Its Predators to Various Enantiomeric Ratios of Ipsdienol and Lanierone in California: Implications for the Augmentation and Conservation of Natural Enemies

Many natural enemies of bark beetles are attracted to bark beetle pheromones, and substantial numbers of them are removed along with the target pests in mass trap-out programs. Thus, additional information on bark beetle and predator behavior is needed to maximize trap-out of target pests while decreasing trapping of beneficial insects. Ips pini (Say) is the most widespread bark beetle associated with pine trees in the United States and Canada. Geographically distant populations vary considerably in their production of, and response to, different stereoisomers of their principal pheromone component, ipsdienol, and an additional pheromone component, lanierone. California populations of I. pini are attracted to 99.9% (-)-ipsdienol, and the presence of lanierone has no effect on attraction. We simulated trap-outs by conducting no-choice assays using three different ratios of (+)/(-) enantiomers of ipsdienol with or without lanierone in the field. Experiments were performed in mixed pine forests in northern California in 1997 and 1998. Experiments were performed twice each year to sample the two major flight periods of I. pini. Ips pini and its predators showed temporal and behavioral differences in their attraction to lures. Lures that are preferred by I. pini, 3(+)/97(-) ipsdienol with or without lanierone, selectively removed up to 5-7 times more pests than predators during early summer. Moreover, the ratios of pest to predators were much higher in the late than early summer, and pest numbers were as much as 282 times higher than predators. In contrast, lures most attractive to predators removed as much as 10 predators for each I. pini trapped. These results suggest that timely applications of carefully selected synthetic lures, in combination with other complementary forest management practices, can greatly improve trap-out programs for bark beetles and natural enemy conservation. In addition, behavioral differences in attraction suggest the potential for augmentation of natural enemies.