Colonization and reproduction of potential competitors with mountain pine beetle in baited logs of a new host for mountain pine beetle, jack pine

The mountain pine beetle (Dendroctonus ponderosae Hopkins) is a bark beetle that is native to pine forests of western North America and the Black Hills of South Dakota. Recent eastward range expansion into stands of jack pine (Pinus banksiana) and associated hybrids with lodgepole pine (Pinus contorta) in western Canada has created concern that the insect will continue moving eastward. In the Great Lakes region, mountain pine beetle would encounter novel species of pines and associated insect fauna; interactions with which are largely unexplored. We baited logs of jack pine with lures for mountain pine beetle and Ips grandicollis (Eichhoff) alone and in combination in a 2 × 2 factorial design in the Black Hills of South Dakota. Both insects occur in this region, but not jack pine, a common species in the Great Lakes region of North America at risk of invasion by mountain pine beetle. We measured attraction and reproduction of insects that colonized the logs. Ips grandicollis were significantly more attracted to logs of jack pine baited with their aggregation pheromone, ipsenol, than unbaited logs or those baited with pheromones of mountain pine beetle and myrcene, a host volatile. Colonization by I. grandicollis was inhibited by the presence of lures for mountain pine beetle. We also found larvae of longhorn borers, likely ­ Monochamus spp., infesting logs. These borers, which act as competitors and facultative predators of bark beetles, were significantly attracted to logs baited with ipsenol over those baited with lures for mountain pine beetle. Our results suggest that if mountain pine beetle were to invade the Great Lakes Region, common bark and wood-boring species such as I. grandicollis and longhorn borers would not compete with mountain pine beetles at tree-colonizing stages, and thus could pose little resistance to invasion.