Agricultural and Forest Entomology (2011), 13, 383–393 DOI: 10.1111/j.1461-9563.2011.00533.x Genetic structure and gene flow among European corn borer populations from the Great Plains to the Appalachians of North America Kyung S. Kim 1 , Brad S. Coates, Mark J. Bagley*, Richard L. Hellmich and Thomas W. Sappington USDA-ARS, Corn Insects and Crop Genetics Research Unit, Genetics Laboratory, Iowa State University, Ames, IA 50011, U.S.A. and * USEPA, NERL, Ecological Exposure Research Division, Cincinnati, OH 45268, U.S.A. Abstract 1 Earlier population genetic spatial analysis of European corn borer Ostrinia nubilalis (H¨ ubner) indicated no genetic differentiation even between locations separated by 720 km. This result suggests either high dispersal resulting in high gene flow or that populations are not in migration–drift equilibrium subsequent to their invasion of the central U.S.A. in the 1940s. 2 To discriminate among these two possibilities, samples were collected at 12 locations in eight states from New York to Colorado, a geographic scale that is three- fold greater than previously tested. Eight microsatellite markers were employed to estimate genetic differentiation and gene flow among these populations, and to test for isolation-by-distance. 3 Although pairwise F ST estimates were very low, there was a significant isolation- by-distance relationship. 4 Wright’s neighbourhood area (i.e. the surface area covered by a panmictic group of individuals within a larger continuous distribution) was calculated as 433 km 2 , and the radius indicates that approximately 13% of O. nubilalis adults disperse a net distance >12 km per generation from their natal source. 5 Analyses indicated significant differentiation between the north-eastern region (New York and Pennsylvania) and the region combining sample locations from Ohio to Colorado, suggesting the potential for isolation of populations by topographic barriers in the Northeast. 6 Taken together, the results suggest that O. nubilalis exhibits substantial gene flow over long distances and that the lack of genetic differentiation between populations across hundreds of kilometres is not simply a result of migration – drift disequilibrium arising from the recent range expansion. Keywords Dispersal, European corn borer, gene flow, genetic structure, invasive, landscape, migration, neighbourhood, Ostrinia nubilalis (Lepidoptera: Crambidae), population genetics. Introduction The European corn borer Ostrinia nubilalis (H¨ ubner) was intro- duced at least thrice to North America from Europe in the early 20th Century (Caffrey & Worthley, 1927), and then proceeded Correspondence: Thomas W. Sappington. Tel.: +1 515 294 9759; fax: +1 515 294 2265; e-mail: tom.sappington@ars.usda.gov 1 Present address: Department of Agricultural Biotechnology, Seoul National University, Seoul 151-742, South Korea. to invade nearly all corn producing regions of the U.S.A. and Canada east of the Rocky Mountains (Showers, 1979; Mason et al., 1996). It is a chronic pest of corn that causes substan- tial losses on an annual basis in many areas, but it is quite difficult to control with chemical insecticides because of its ability to bore into the stalk where it is sheltered from contact sprays (Mason et al., 1996; Rice & Pilcher, 1998). The intro- duction of transgenic Bacillus thuringiensis (Bt) corn in the U.S.A. in 1997 has revolutionized O. nubilalis management, Published 2011. This article is a U.S. Government work and is in the public domain in the USA.