Mechanisms driving flight polyphenisms in the mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae: Scolytinae)

The mountain pine beetle (Dendroctonus ponderosae) is an important forest pest in Western North America that is currently undergoing range expansion.  The mountain pine beetle exhibits polyphenic variation in flight capability but the mechanisms maintaining this variation are unknown. This study tested the effect of flight on: (1) host colonisation capacity; and (2) pheromone production after host entry. A subset of beetles was subjected to a flight treatment using a computer-linked flight mill assay.  Both flown and unflown (control) beetles were subsequently given the opportunity to colonise bolts of host trees, and beetles that entered hosts were aerated to collect pheromone. We detected a trade-off between host colonisation and flight that was driven by the percent body weight lost during flight.  This indicates that energy-use during flight affects host utilization by female mountain pine beetles. Furthermore, production of the aggregation pheromone trans-verbenol by female beetles was influenced by both percent weight lost during flight and flight distance. Male production of exo-brevicomin was affected by beetle condition following flight but not by energy use during flight. These novel results give insight into the polyphenic flight behavior of mountain pine beetles. We suggest mechanisms that facilitate the extremities of the continuous flight polyphenism spectrum in mountain pine beetles.