Complexities in predicting mountain pine beetle and spruce beetle response to climate change

Abstract Mountain pine beetle (Dendroctonus ponderosae) and spruce beetle (D. rufipennis) are two significant native tree mortality agents with expansive distributions throughout North America. The range of spruce beetle is considered coincident with Picea across North America. Although the distribution of mountain pine beetle in Pinus forests has historically been restricted by climate, recent warming has accelerated migration northward in western Canada. Both species are being directly influenced by changes in climate, particularly warming temperatures that can reduce winter mortality and shorten lifecycles from one generation every 2 years to one generation every year. The two species are similar in development rates, and they both have diapause states in two life stages that serve to synchronize cohorts with appropriate seasons, although diapause in mountain pine beetle is more variable and less prevalent than in spruce beetle. We review thermally dependent traits in both species and discuss how evolved physiological processes could both promote and restrict population success of the two species as climate continues to change.