Successful colonization, reproduction, and new generation emergence in live interior hybrid spruce Picea engelmannii × glauca by mountain pine beetle Dendroctonus ponderosae

1 Although mountain pine beetle Dendroctonus ponderosae Hopkins are able to utilize most available Pinus spp. as hosts, successful colonization and reproduction in other hosts within the Pinaceae is rare. 2 We observed successful reproduction of mountain pine beetle and emergence of new generation adults from interior hybrid spruce Picea engelmannii × glauca and compared a number of parameters related to colonization and reproductive success in spruce with nearby lodgepole pine Pinus contorta infested by mountain pine beetle. 3 The results obtained indicate that reduced competition in spruce allowed mountain pine beetle parents that survived the colonization process to produce more offspring per pair than in more heavily-infested nearby pine. 4 We also conducted an experiment in which 20 spruce and 20 lodgepole pines were baited with the aggregation pheromone of mountain pine beetle. Nineteen pines (95%) and eight spruce (40%) were attacked by mountain pine beetle, with eight (40%) and three (15%) mass-attacked, respectively. 5 Successful attacks on nonhost trees during extreme epidemics may be one mechanism by which host shifts and subsequent speciation events have occurred in Dendroctonus spp. bark beetles.