Associations of secondary bark beetles with dying and live lodgepole pine in the post-outbreak phase of mountain pine beetle, Dendroctonus ponderosae (Hopkins), in the central interior of British Columbia, Canada.

Dendroctonus ponderosae (Hopkins) or mountain pine beetle is a native bark beetle (Coleoptera: Curculionidae: Scolytinae) that feeds on more than 20 species of pine in western North America. In British Columbia, its principal host is lodgepole pine (Pinus contorta var. latifolia Engelmann). As a primary bark beetle, D. ponderosae kills its host at epidemic stages, exerting profound landscape-level mortality. As of 2012, D. ponderosae has caused the loss of 726 million cubic meters of timber, covering an area of 17.5 million hectares of mature pine forest in British Columbia and Alberta. Small diameter hosts are not suitable for D. ponderosae, however, creating a niche for the secondary bark beetles, including Ips pini (Say), Pseudips mexicanus (Hopkins), and Orthotomicus latidens (LeConte). At the post-epidemic stage of D. ponderosae, we found the rate of new mortality was approximately 4%, which 1% of the mortality was associated with a complex of secondary bark beetles, and not D. ponderosae, as the principal mortality agent in those stands. This finding suggests that at high population densities, secondary bark beetles are potential mortality agents of residual pines, sustaining the apparent outbreak of D. ponderosae by killing smaller diameter trees, with the highest rate of mortality among younger stands. --P. ii.