Mountain pine beetle: an example of a climate-driven eruptive insect impacting conifer forest ecosystems.

Climate change is altering the survival and reproductive capacity of plant-feeding insects in multiple ecosystems worldwide, in some cases creating conditions highly suitable for population eruptions. Forest ecosystems are particularly sensitive to climate change as their vulnerability is manifested, in part, as an upsurge in natural disturbances such as native insect outbreaks. The mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), is a phloem-feeding bark beetle indigenous to western North America that attacks most species of pine including its major hosts, lodgepole pine and ponderosa pine. Adult mass aggregation, mediated by pheromones, helps the beetle to overcome tree defenses eventually killing the tree. Recent outbreaks of this insect have caused extensive pine mortality and have affected millions of hectares of forested area in western North America. Climate is a major driver of these outbreaks. In this review, we describe the direct influences of various climate-related factors on MPB development, outbreak behavior, and range expansion and their indirect impact on MPB epidemiology via influences on host trees and MPB-associated fungi. We also underscore the ecological and economic consequences of the recent, unprecedented MPB outbreak. Of serious concern currently is whether climate change will facilitate rapid establishment and spread of MPB in naïve pine forests. MPB will likely adapt quickly to new thermal environments under climate change given its short generation time; however, uncertainties and gaps in our understanding of MPB population dynamics (e.g., trophic interactions) in newly invaded habitats preclude an accurate assessment of outbreak potential and spread at this time.