Predators and competitors of the mountain pine beetle Dendroctonus ponderosae (Coleoptera: Curculionidae) in stands of changing forest composition associated with elevation

Abstract

Abstract The mountain pine beetle Dendroctonus ponderosae (Coleoptera: Curculionidae) is an irruptive tree‐killing bark beetle native to pine stands in western North America. The primary hosts are lodgepole and ponderosa pines. Recent rising temperatures, however, have allowed these beetles to survive at higher elevations more commonly than in the past, thus threatening whitebark pine, a keystone species of high elevation ecosystems and a highly susceptible host. The extent to which risk in whitebark pine stands may be mitigated by predators or competitors is unknown. We compared the communities of coleopteran predators and competitors of D. ponderosae in sites of varying elevation and species composition in Montana and Wyoming, U.S.A. Sites were selected for low to moderate levels of tree mortality, where the potential of natural enemies to prevent D. ponderosae from transitioning into outbreaks would be most relevant. Insect populations were evaluated using unbaited flight‐intercept panel traps and pheromone‐baited multiple funnel traps. Only the predatory beetle species Thanasimus undatulus (Coleoptera: Cleridae) was captured in these non‐outbreak stands. Based on the pheromone‐baited traps, predator load was higher at low‐elevation stands dominated by lodgepole pine than high‐elevation stands dominated by whitebark pine. Phloeophagous insects were more prevalent in the mid‐ and higher‐elevation sites, although most of the species captured would not likely compete substantially for resources with D. ponderosae. We also observed differences in species assemblages between the Montana and Wyoming sites, as well as differing utilities of baited and unbaited traps at low versus moderate tree mortality levels.