Conclusions
Here we find that winter moth is a serial invader of North American forests and orchards, with at least four introductions from Europe. These populations were introduced from a diversity of locations in Western and Central Europe. Most notable is the fact that populations in Nova Scotia and the Northeastern United States are genetically distinct from each other, despite having only ~ 300 km separating surveyed populations in Maine and Nova Scotia. Given the availability of a sequenced genome (Derks et al., 2015), and its historical use in population ecology (Varley & Gradwell 1960; Varley et al., 1973), we hope that our work encourages the use of winter moth as a model organism for comparative studies of the genomic factors that influence the establishment of invasive species. Lastly, we hope that our method for the interpretation of Structure results can provide rapid and accurate inferences into the geographic regions of origins of non-native species.