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Spatial and temporal genetic analyses reveal high gene flow among European corn borer (Lepidoptera: Crambidae) populations across the central U.S. cornbelt
Citation:
Kim, K. S., M. J. BAGLEY, B. S. Coates, R. L. Hellmich, AND T. W. Sappington. Spatial and temporal genetic analyses reveal high gene flow among European corn borer (Lepidoptera: Crambidae) populations across the central U.S. cornbelt. ENVIRONMENTAL ENTOMOLOGY. Entomological Society of America, Lantham, MD, 38(4):1312-1323, (2009).
Impact/Purpose:
This research effort is designed to provide the risk assessment community with modern genetic tools for evaluating long-term risks of genetically modified (GM) crops. Molecular population genetic data can potentially reveal information about long-term trends in both pest populations targeted by plant-incorporated pesticides (PIPs) and non-target populations. EPA regulations require specific pest management strategies to slow the evolution of resistance in target pest populations in order to prolong the environmental benefits of GM crops (i.e., reduced use of chemical pesticides). A key component of this research effort will be to provide detailed information on pest biology, including gene flow and mating patterns in the wild (within species and between closely related species), geographic and chromosomal distribution of resistance alleles, and the additive and non-additive effects of genetic variation on resistance under selective pressures in the field. These data will be used to improve and validate models of insect resistance development with the goal of implementing best agricultural practices for delaying or preventing the development of pest resistance. These methods will be evaluated as a necessary component in the process of developing novel PIPs. Monitoring resistance in the field is also a key component of Bt-crop stewardship mandated by the EPA. We will develop potential resistance markers using candidate resistance genes. Potential resistance markers will be used to develop a rapid molecular screening tool for field analysis of resistance in the field. Molecular monitoring would be preferable over regular field monitoring of crop damage due to resistant insects since molecular monitoring can detect resistance before economic damage and before resistance is wide spread. Molecular monitoring can potentially be an early indicatory of resistance development and allow time for remediation efforts.
Description:
European corn borer, Ostrinia nubilalis (Hubner), adults were sampled at 13 sites along two perpendicular 720-km transects intersecting in central Iowa, and for the following two generations at four of the same sites separated by 240-km in the cardinal directions. More than 50 moths from each sample location and time were genotyped at eight microsatellite loci. Spatial analyses indicated that there is no spatial genetic structuring between European corn borer populations sampled 720 km apart at the extremes of the transects, and no pattern of genetic isolation by distance at that geographic scale. Although these results suggest high gene flow over the spatial scale tested, it is possible that populations have not had time to diverge since the central Corn Belt was invaded by this insect about 60 years ago. However, temporal analyses of genetic changes in single locations over time suggest that the rate of migration is indeed very high. The results of this study suggest that the geographic dimensions of European corn borer populations are quite large, indicating that monitoring for resistance to transgenic Bt corn at widely separated distances is justified, at least in the central Corn Belt. High gene flow further implies that resistance to Bt corn may be slow to evolve, but once it does develop it may spread geographically with such speed that mitigation strategies will have to be implemented quickly to be effective.