Reconstructing the geographic origins of invasive species is critical
for establishing effective management strategies. Frequently, molecular
investigations are undertaken when the source population is not known,
however; these analyses are constrained both by the amount of diversity
present in the native region and by changes in the genetic background of
the invading population following bottlenecks and/or hybridization
events. Here we explore the geographical origins of the invasive winter
moth (Operopthera brumata L.) that has caused widespread defoliation to
forests, orchards, and crops in four discrete regions: Nova Scotia,
British Columbia, Oregon, and the northeastern United States. It is not
known whether these represent independent introductions to North
America, or “stepping stone” spread among regions. Using a combination
of Bayesian assignment and approximate Bayesian computation methods, we
analyzed a population genetic dataset of 24 polymorphic microsatellite
loci. We estimate that winter moth was introduced to North America on at
least four occasions, with the Nova Scotian and British Columbian
populations likely being introduced from France and Sweden,
respectively; the Oregonian population likely being introduced from
either the British Isles or northern Fennoscandia; and the population in
the northeastern United States likely being introduced from somewhere in
Central Europe. To our surprise, we found that hybridization has not
played a large role in the establishment of winter moth populations even
though previous reports have documented widespread hybridization between
winter moth and a native congener. We discuss the impact of genetic
bottlenecks on analyses meant to determine region of origin.
Four times out of Europe: serial invasions of the winter moth, Operophtera brumata, to North America
