Researchers in Wisconsin and California have worked with a common bark beetle, the pine engraver, Ips pini, that occurs in much of North America. The bark beetles produce slightly different pheromones in the two states. In each location the scientists used caged logs baited with beetles from both states. In both locations, the dominant predators (a clerid beetle in California and a hister beetle in Wisconsin) were significantly more attracted to the logs containing beetles from the opposite state. The research has several implications for biological control. For example, the reciprocal introduction of natural enemies to locations where they are most attracted to the prey would be a form of classical biological control but using native natural enemies. Another implication is for bark beetle pheromone trapout programs using the correct pheromone chemistry would reduce the impact on native predators.
Raffa, K. F. and D. L. Dahlsten. 1995. Differential responses among natural enemies and prey to bark
beetle pheromones. Oecologia 102:17-23.