How climate change and host-specific cold tolerance may mediate invasion potential of mountain pine beetle (Dendroctonus ponderosae) in novel eastern forests

The mountain pine beetle (Dendroctonus ponderosae, Hopkins) is an aggressive bark beetle native to western North American and able to kill large areas of pine forests during outbreaks. This insect is a potential threat to pines in eastern North American forests due to an ongoing eastward range expansion through the boreal forest of Alberta. Alternatively the insect could be introduced by movement of infested logs from outbreak regions. While the eastern extent of the insect’s range is only 650km from eastern pine forests of the Great Lakes region, the beetle has never become established east of the Great Plains. Here we assess whether climate and host specific cold tolerance may affect establishment in eastern pine forests. We tested the cold tolerance of mountain pine beetles reared in two native (lodgepole and ponderosa) and four novel eastern and Eurasian hosts (jack, red, eastern white and Scots pine). We further analyzed 50 years of minimum winter temperatures across the western Great Lakes region. Our results indicate that a combination of reduced cold tolerance of the insect in some novel eastern hosts and cold minimum winter temperatures in the western Great Lakes region may have been factors in the insect’s inability to establish in this region in the past. However, we also show that minimum winter temperatures across the region have become increasingly suitable in the last 50 years, with a reduced likelihood of winters capable of causing complete mortality, particularly amoung beetles in some of the most cold tolerant hosts.