The European corn borer, Ostrinia nubilalis (Hu¨ bner), causes economic damage to corn, Zea mays L., throughout the Corn Belt. Because this insect has become the primary target of Bacillus thuringiensis Berliner (Bt) transgenic corn, current efforts addressing the management of O. nubilalis resistance to Bt corn require information on adult European corn borer dispersal and factors affecting its dispersal. In 1998 we conducted markÐreleaseÐrecapture, releaseÐrecapture, and caged-mating studies to directly measure and compare local dispersal patterns of O. nubilalis adults within and proximal to irrigated and non-irrigated cornÞelds. Releases of marked adults were made corresponding to the Þrst and second ßight of O. nubilalis in eastern Nebraska. Adult dispersal was signiÞcantly different between irrigated and non-irrigated cornÞelds. Released adults tended to remain in and near irrigated cornÞelds, but dispersed out of and away from non-irrigated cornÞelds. When released at the edge of the cornÞeld, neither male nor unmated female O. nubilalis displayed an initial tendency to move out of irrigated corn and into the mixed smooth bromegrass (Bromus inermis Leyss) and broadleaf-weed Þeld edge. Mating efÞciency in a late-season cornÞeld was not signiÞcantly different than in dense foxtail (Setaria spp.). Generally, we found that adult O. nubilalis dispersal may vary depending on variables such as action-site availability and agronomic practices and their interaction with O. nubilalis life history.