The mountain pine beetle Dendroctonus ponderosae (Curculionidae: Scolytinae) (MPB) is one component of an intensively studied co-evolved insect–host system. We investigated the spatial genetic structure of the MPB within its historic and recent geographic range expansion as it relates to host use in western North America using 13 pre-selected microsatellite loci. Analysis of molecular variation (AMOVA) indicates that genetic structure is not correlated with the host tree species and therefore does not support the hypothesis of the formation of a host race within this species. STRUCTURE analysis delineates four main clusters in western North America: (1) northern: northern British Columbia/northern Alberta; (2) central: southern British Columbia/southern Alberta/Washington/Idaho/Montana; (3) southwestern: Oregon/California/Nevada; and (4) southeastern: Utah/Wyoming/Arizona/Colorado/South Dakota. Heterozygosity, allelic richness, and the number of private alleles are greatest in the Southwest cluster. This cluster correlates with one of the three refugia hypothesized from a recent analysis of neo-Y haplotypes and represents an important reservoir of MPBs’ genetic diversity.

The mountain pine beetle (MPB) is one component of an intensively studied co-evolved host-pest system. We investigated the spatial genetic structure of MPB within its historic and recent geographic range expansion as it relates to host use in western North America using 13 pre-selected microsatellite loci. AMOVA shows that genetic structure is not correlated with the host tree species, arguing against the formation of host-race within this species. STRUCTURE analysis shows 4 main clusters in western North America: Northern - Northern British Columbia/Alberta; Central - Southern British Columbia/Alberta/Washington/Idaho/Montana; Southwest - Oregon/California/Nevada and; Southeast - Utah/Wyoming/Arizona/Colorado/South Dakota. Heterozygosity, allelic richness, and number of private alleles is greatest in the Southwest cluster. This cluster correlates with one of the three refugia hypothesized from a recent analysis of neo-Y haplotypes by Dowle and colleagues and represents an important reservoir of MPB genetic diversity.