Sample collection
Winter moth males were collected using pheromone-baited traps (Elkinton et al., 2010; Elkinton, Lance, Boettner, Khrimian, & Leva, 2011) from locations in Europe, North Africa, and western Asia, as well as from the four regions in North America, where established winter moth populations have been recorded (Nova Scotia, British Columbia, Oregon, and the northeastern United States, Figure 1). In addition, larval individuals and adult females, which are wingless and do not fly, were opportunistically collected (see supplemental Appendix S1 Table S1 for complete collection information, including life stages).
After collection, adult moths were placed in glassine envelopes (Uline Corporation, USA) and stored at either -20°C or -80°C, and larval caterpillars were placed in 95% ethanol and stored at -20°C. For many of the moths included in our analysis, collection and genotype information was previously reported (e.g., Andersen, Havill, Caccone, & Elkinton, 2017; Andersen et al., 2019a,b, In Press) (Supplemental Appendix S1 Table S1).