Gene flow and genetic structure of European corn borer (Ostrinia nubilalis) e- and z-pheromone races in the northeastern US: Greater isolation of e-race populations

As a serious and widely distributed economic pest of corn production in North America, European corn borer (Ostrinia nubilalis) (ECB) is now largely managed with transgenic Bt corn.  Although Bt-resistance monitoring efforts are focused in the Corn Belt where corn acreage is the highest, a greater danger of resistance development may lie in the Northeast. There, the varied topography, isolated cornfields, as well as sympatric populations of partly reproductively isolated pheromone races (E and Z) of ECB, may restrict gene flow allowing resistance to evolve more quickly. In this project we are investigating gene flow and genetic structure within and between ECB E-race and Z-race populations in New York and Pennsylvania using 60 SNP markers. Despite the high gene flow both within and between races, we found greater population connectivity among Z-race populations than among E-race populations, and greater within race population connectivity than between races. However, connectivity is found among some populations of different races at the same location in the same year, suggesting that the reproductive isolation by pheromone system is not very strong. The results of our study indicate E-race ECB are more likely to have isolated populations, and thus are at higher risk of evolving Bt resistance. Furthermore, the spread of resistance that develops in one race to the other race may occur rapidly in the absence of strong reproductive isolation by pheromone system. Therefore, monitoring for Bt resistance in the Northeastern US may be justified.