Submitted to: Agricultural and Forest Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/27/2011
Publication Date: 5/5/2011
Citation: Kim, K., Coates, B.S., Bagley, M.J., Hellmich II, R.L., Sappington, T.W. 2011. Genetic structure and gene flow among European corn borer populations from the Great Plains to the Appalachians of North America. Agricultural and Forest Entomology. 13(4):383-393. Interpretive Summary: The European corn borer (ECB) is a major pest of corn in the U.S. and is the main target of transgenic Bacillus thuringiensis (Bt)-corn expressing the Cry1Ab toxin. Because of the high use of Bt-corn, there is worry that this insect will develop resistance to it, so scientists must continually monitor populations across the U.S. for resistance. It is important to choose the most appropriate distance between sites needed for adequate monitoring, which is determined by the distance European corn borer moths disperse per generation. Results of a previous study in the central U.S. Corn Belt suggest that the geographic dimensions of ECB populations may be quite large, but there is some question about just how large they are. To answer this question, we expanded the geographic scale of sampling to 12 populations across eight states from New York in the east to Colorado in the west, a geographic scale 3-fold greater than previously tested. We used molecular genetic markers to estimate how closely related these populations are to one another genetically, which in turn can be used to estimate how far European corn borer moths tend to fly per generation. Our analyses indicate that 1000 ECB moths per generation are expected to move between locations separated by 83 km, and 150 moths are expected to move between locations separated by 1000 km. Dispersal over such great distances has major implications for insect resistance management strategies for European corn borer in transgenic Bt-corn. This information will be of use to officials in regulatory agencies responsible for resistance management regulations for Bt crops. It also will be useful to university, government, and industry scientists and modelers trying to understand and predict rates of resistance development in European corn borer to Bt-corn.
Technical Abstract: Earlier population genetic spatial analysis of European corn borer (ECB), Ostrinia nubilalis, populations sampled along transects indicated, surprisingly, that there is no genetic differentiation between populations separated by as much as 720 km. This unanticipated result suggests either that European corn borer are much more mobile than expected resulting in high gene flow, or that they remain undifferentiated since the range expansion that brought them from the eastern U.S. to Iowa in the 1950s. To discriminate between these two possibilities, samples were collected from 12 locations in eight states during 2007 from New York in the east to Colorado in the west, a geographic scale 3-fold greater than previously tested. Eight microsatellite markers were employed to estimate genetic differentiation and gene flow among these populations, and to calculate isolation by distance. Although pairwise FST's were very low even at this extended geographic scale, there was a significant isolation by distance pattern. The results suggest that dispersal is very high in this insect and not an artifact of the range expansion. Our analyses indicate that 1000 ECB moths per generation are expected to move between locations separated by 83 km, and 150 moths are expected to move between locations separated by 1000 km. Dispersal over such distances has major implications for insect resistance management strategies for European corn borer in transgenic Bacillus thuringiensis (Bt)-corn.