Thermal suitability of the western great lakes region for persistence of mountain pine beetle (Coleoptera: Curculionidae)

Mountain pine beetle (Dendroctonus ponderosae Hopkins) is a bark beetle native to western North America. During outbreaks it frequently kills mature pines. This beetle is currently responsible for the largest ongoing forest insect outbreak on record, affecting lodgepole and ponderosa pine across the Rocky Mountain region. Of critical concern is eastward expansion through jack pines of Canada’s boreal forest into the north central region of the United States. Anthropogenic movement of infested material to the Great Lakes region from nearby outbreak areas such as western South Dakota could inadvertently introduce this insect. Thermal regimes play a key role in determining MPB range limits. In this study, we assess the suitability of temperatures for persistence of mountain pine beetle in the western Great Lakes region.  Fifty years of daily maximum and minimum temperature records (1962-2012) from pine regions in Minnesota were collected. We show that Minnesota’s thermal regime is becoming increasingly suitable for MPB persistence. Degree day requirements for development and average temperatures needed for flight and host procurement activity are consistently above the minimum thresholds. The likelihood of complete winter mortality due to extreme cold temperatures, while possibly a deterrent to establishment in the past, is becoming less probable due to a decadal warming trend. Some forested areas have not experienced these extreme cold temperatures in the last 50 years. These results suggest that temperature regimes may not strongly inhibit MPB establishment should it reach the western Great Lakes region, a gateway to the pine forests of the eastern United States.