Improved Population Monitoring of Bark Beetles and Predators by Incorporating Disparate Behavioral Responses to Semiochemicals

Estimating populations of both pest and natural enemy species is important in the planning and implementationof biological control. For example, synthetic pheromone lures are used to sample bark beetles, and sometimes their predators, in forest ecosystems. However, insect attraction to natural pheromone sources may differ from attraction to synthetic pheromone lures. Moreover, these differences may vary systematically between the target pest and some important natural enemies. Thus, the accuracy of both absolute and relative abundances of bark beetles and predators could varywith lure selection.We evaluated a series of synthetic lures to determinewhich lure gave the closest approximation to actual numbers of Ips pini (Say) andpredators arriving at hosts infested with I. pini in Wisconsin. We deployed synthetic lures containing various ratios of the (1) and (2) enantiomers of the principal I. pini pheromone component, ipsdienol, with or without an additional component, lanierone. I. pini showed strong preferences for speciÞc enantiomeric ratios of ipsdienol, and these responses were synergized by lanierone. Predators showed equally strong attraction to ipsdienol, but preferred different ratios of the stereoisomers. The addition of lanierone had no effect on predators. The most abundant predator, Thanasimus dubius (F.), showed greater preference for host material infested with I. pini than any synthetic lure. These disparities in responses, combined with strong disparities in seasonal ßight patterns, provided estimates of pest to predator ratios that varied by as little as 12% to asmuch as 12 times, frompest:predator ratios arriving athostmaterial infestedwith I. pini.These results suggest that variationbetweenherbivores and their natural enemies in their phenology, preferred pheromone blends, and infested host material should be considered when developing estimates of relative pest and predator densities for subsequent management options.