Chemical similarity between introduced and native populations of Scots pine can facilitate transcontinental expansion of mountain pine beetle in North America

Introduced forest tree species are frequently attacked by insects in their new range; however, it has been seldom investigated whether the presence of such tree species increases the risk of range expansion of native insect herbivores in the introduced range. European Scots pine has been introduced to North America including within a portion of the range of the mountain pine beetle (MPB). We investigated Scots pine suitability to MPB as a host in the introduced range of the pine populations. We compared chemotypic similarity of foliage between introduced and native Scots pine populations, and then determined the suitability of introduced populations to MPB. Suitability was assessed based on whether beetles produce aggregation pheromone components and complete development in Scots pine bolts. We also assessed whether or not suitability was affected by the host chemotypes. Introduced and native pine populations had the same sesquiterpene chemotypes and shared one of the two monoterpene chemotypes. All introduced populations were suitable for MPB but the suitability varied slightly with host chemotype. This is the first report of chemotypic variations of Scots pine populations outside its native range. Chemotypic similarity between the introduced and native pine populations, ability of beetles to produce pheromones and to complete its life cycle on bolts from all chemotypes, and preferential colonization of Scots pine over native pine species by MPB in field suggest that introduced Scots pine populations could facilitate transcontinental expansion of MPB in North America.