Genetic structure of the forest pest Hylobius abietis on conifer plantations at different spatial scales in Europe.

The distribution of genetic variation within and among 20 European sites infested by the large pine weevil, Hylobius abietis, was analysed using dominant amplified fragment length polymorphism markers. Analysis of molecular variance was performed at the European, regional and local scales. Most of the genetic variability was found within rather than among populations and the global fixation index averaged over loci was low (0.07). We found no evidence of genetic drift, even in relatively isolated sites. This genetic pattern tends to confirm the high dispersal ability of the weevil and the influence of human-mediated expansion of its range through conifer plantations across Europe since the 19th century. Assignment tests demonstrated that the regional forest is a pertinent geographic scale for defining populations in the large pine weevil. Testing the potential influence of the larval host-plant identity (Scot Pine vs Norway Spruce) on the genetic structure revealed a weak but significant effect in two of the three regions tested (in Ardèche and in Limousin but not in Finland). One locus varied with host-plant use in the two French regions, indicating a potential role in host-plant adaptation. However, host-race formation is not observed in H. abietis; we discuss this result in the light of our current knowledge of this insect's biology. Altogether, this study shows that the use of different host plants for development does not constitute a strong barrier to gene flow for H. abietis and confirms the high dispersal ability of this forest pest.