Forestry News

Bark Beetle Predators Smell Their Prey

An important characteristic of effective natural enemies is their ability to locate their hosts or prey (the pest). Good biological control agents are able to locate and feed on their prey when that prey is at low numbers. This helps keep the pest population from increasing. Different natural enemies have different ways of locating their prey, but a common method is by smell. Plant feeding pests emit a variety of odors, including sex attractants or sex pheromones. These chemicals are used by a member of one sex to attract mates. Many natural enemies have evolved to recognize the pheromones of their prey and use this for prey location. However, in the constant coevolution between predator and prey, the prey will evolve slightly different pheromone chemistry that is not as attractive to the predator.

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.

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