Pheromone surveys
In Massachusetts, for each year from 2007-2018, adult male moths were collected using pheromone-baited lures (Great Lakes IPM, Vestaburg, MI; Elkinton et al., 2010, 2011) hung in plastic bucket traps (Gempler’s Inc., Janesville, WI) at points along the Massachusetts transect (Figure 1). These included 49 unique localities; however, due to factors such as road construction, early-season snow, ice storms, vandalism, and mouse predation, an average of 22 trap localities (± 1.5) were sampled each year, with a minimum of 16 traps in 2015 and a maximum of 32 traps in 2017 and 2018. In addition, after 2009, we discontinued monitoring traps close to the Boston Metropolitan area (T21-T25) in an effort to conserve survey resources because these traps were entirely composed of winter moth individuals (Elkinton et al., 2014). From 2007-2016, moths were collected from traps twice during the sampling period (late November through early January), coinciding with observations of male moth flight. In 2017, moths were collected during the same period weekly, and in 2018, traps were sampled bi-weekly. For the Connecticut transect (Figure 1), pheromone traps were deployed from 2016-2018. These included 19 localities in 2016, though due to factors mentioned above, in 2017 and 2018, only 18 and 17 of these localities were sampled, respectively. Along this transect, moths were collected weekly from late November through early January. A list of trap locations is provided in Supplemental Table S1. Upon collection, moths were removed from traps, placed in glassine envelopes (Uline Inc., Pleasant Prairie, WI), and stored at -80°C. The total number of moths collected over the flight period in each trap was counted to provide an estimate of relative population density surrounding each trap location.