Potential for biological control of native North American Dendroctonus beetles (Coleoptera: Scolytidae)
Bark beetles of the genus Dendroctonus inflict serious damage in North American coniferous forests. Biological control, which has never been seriously attempted with bark beetles in the United States, should be reconsidered in light of results disclosed here. Impact of indigenous associates is discussed, as well as previous, unsuccessful attempts to introduce exotic enemies. Potential of insect enemies of allied pests is considered in light of Pimentel's theory of "new associations." Extraregional and exotic bark beetle predators from different forest ecosystems are shown to be able to detect aggregating pheromones (kairomones) of beetles related to their normal prey. Some guidelines for necessary experiments before new introductions are discussed, and two examples are reported. One involves a North American clerid, Thanasimus undatulus Say, a predator of the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, which responded to pheromones in cross-attraction field tests. The other involves the palearctic beetle, Rhizophagus grandis Gyllenhal, a specific predator of D. micans Kugelann. In laboratory bioassays, R. grandis was attracted to frass of three North American Dendroctonus. Because predators like T. undatulus and R, grandis may be able to locate infestations of other Dendroctonus, they are potential biological control agents. This research shows that trapping with aggregating pheromones in the habitat of related pests and field and laboratory olfactometric experiments are both useful in screening for potential insect biological control agents.