The mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae) is a major forest pest of pines in western North America. Beetles typically undergo a one-year life cycle with larval cold hardening in preparation for overwintering. Two-year life cycle beetles have been observed but not closely studied. This study tracks cold-hardening and preparation for overwintering by adult mountain pine beetles in their natal galleries. Adults were collected in situ between September and December 2016 for a total of nine time points during 91 days. Concentrations of 41 metabolites in these pooled samples were assessed using quantitative nuclear magnetic resonance (NMR). Levels of glycerol and proline increased significantly with lowering temperature during the autumn. Newly eclosed mountain pine beetles appear to prepare for winter by generating the same cold-tolerance compounds found in other insect larvae including mountain pine beetle, but high on-site mortality suggested that two-year life cycle adults have a less efficacious acclimation process. This is the first documentation of cold acclimation metabolite production in overwintering new adult beetles and is evidence of physiological plasticity that would allow evolution by natural selection of alternate life cycles (shortened or lengthened) under a changing climate or during expansion into new geoclimatic areas.

The mountain pine beetle (Dendroctonus ponderosae Hopkins) (Coleoptera: Curculionidae) is a significant destructive force in the pine forests of western Canada and has the capacity to spread east into a novel host tree species, jack pine (Pinaceae). New populations have been documented in central Alberta, Canada, but the source populations for these outbreaks have yet to be identified. In this study, we use genetic data to identify parent populations for recent outbreak sites near Slave Lake, Lac La Biche, and Hinton, Alberta. We found the northern population cluster that entered Alberta near Grande Prairie was the source of the most eastern established population near Lac La Biche, and the range expansion to this leading-edge population has been too rapid to establish evidence of population structure. However, some dispersal from a population in the Jasper and Hinton area has been detected as far north and east as Slave Lake, Alberta. We also identified two potential source populations for the current outbreak in Hinton: most beetles appear to be from Jasper National Park, Alberta, but some also originated from the northern population cluster. These findings demonstrate the dynamic dispersal capabilities of mountain pine beetle across the Alberta landscape and the potential hazard of increased dispersal to newly established leading-edge populations.

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, Dendroctonus ponderosae (Coleoptera: Curculionidae) is a major forest pest of pines in western North America. Beetles typically undergo a one-year life cycle with larval cold hardening in preparation for overwintering. Two-year life cycle beetles have been observed but not closely studied. This study tracks cold-hardening and preparation for overwintering by adult MPB in their natal galleries. Adults were collected in situ between September and December (2016) for a total of nine time points during 91 days. Concentrations of 41 metabolites in these pooled samples were assessed using quantitative NMR. Levels of glycerol and proline increased significantly with lowering temperature during the autumn. Newly eclosed mountain pine beetles prepare for winter by generating the same cold-tolerance compounds found in larvae, but high on-site mortality suggested that two-year life cycle adults have a less efficacious acclimation process. This is the first documentation of cold acclimation metabolite production in overwintering new adult beetles and is evidence of physiological plasticity that would allow evolution by natural selection of alternate life cycles (shortened or lengthened) under a changing climate or during expansion into new geoclimatic areas.

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.

Mountain pine beetles began to appear at epidemic levels in Alberta, Canada, in 2006, following six years of extensive outbreaks in neighboring British Columbia. We assessed the effect of genetic MPB in-flights from the peak of the outbreak on the genetic structure of established populations of MPB and the change over time in novel regions colonized by these inflights. We used five locations sampled during the peak of the outbreak (2005/2007) and re-sampled in 2016. We performed a ddRADseq protocol to generate a SNP dataset via single-end Illumina sequencing. We detected a northern and southern genetic cluster in both sampling sets (2005/2007 and 2016) and a demographic shift in cluster assignment after ∼10 generations from south to north in two of the sites in the path of the northern outbreak. Fst values were significantly different between most sites in the same years and between the same sites at different years, with some exceptions for northern sites established by inflights. Overall, sites in the spreading path of the MPB outbreak have taken on the genetic structure of the contiguous northern outbreak except for an isolated site in Golden, BC, and in Mount Robson Provincial Park where populations are admixed between north and south. Our results suggest that range expansion during insect outbreaks can alter the genetic structure of established populations and lead to interbreeding between populations.