Comparisons of mountain pine beetle (Dendroctonus ponderosae Hopkins) reproduction within a novel and traditional host: Effects of insect natal history, colonized host species and competitors

During host-breadth expansion, phytophagous insects incur risk from potentially deleterious novel host environments at the same time as potentially securing a potential escape in space or time from competing species. Bark beetles reproduce under the bark of stems and branches of mature, stressed or moribund trees, and may suffer high mortality from plant defences and inter- and intraspecific competition. An epidemic of mountain pine beetle (Dendroctonus ponderosae Hopkins) in western Canada has extended to over 18.1million hectares of lodgepole pine (Pinus contorta Douglas ex. Loudon) forests. In some areas, mountain pine beetles have been found to reproduce within interior hybrid spruces [Picea glauca (Moench) Voss × engelmannii Parry ex. Engelmann], a normally rare occurrence. Using mountain pine beetles reared from naturally-infested interior hybrid spruce and lodgepole pine hosts, we examined the effect of female natal species and colonized host species on the ability to attract mates and reproduce within spruce and pine logs deployed as a choice assay in a field setting. Additionally, we examined whether the arrival and reproduction of competitors such as pine engravers (Ips spp.) was associated with reduced brood production. Females reared from pine and spruce exhibited similar reproductive potentials. Recruitment and establishment of ovipositional galleries, larval galleries and pupal chambers were similar in the typical and novel hosts. Reproduction by mountain pine beetles in spruce, although successful, was significantly lower than in pine. This reduction occurred despite spruce logs being almost entirely free of competing secondary beetles.