Microsatellite loci characterized from Helicoverpa zea are being used as genetic markers to reveal temporal and spatial variation in the genetic structure and migration patterns of adults caught in pheromone traps. Temporal changes in genetic differentiation are being measured from moths caught over the course of two years at weekly intervals for the same, local sites in Pennsylvania. Stable carbon isotope ratios are also being measured to narrow the potential host plant source of these moths. Spatial changes in genetic differentiation are being measured from moths caught at regional sites in the USA over the course of the 2005 growing season. Understanding the interaction of migration and gene flow in H. zea is needed for development of effective management strategies aimed at reducing resistance to insecticides and transgenic crops.