Genetic structuring of western corn rootworm (Coleoptera: Chrysomelidae) populations in the United States based on microsatellite loci analysis

The western corn rootworm (Diabrotica virgifera virgifera LeConte) (Coleoptera: Chrysomelidae) is a major corn insect pest in North America and is spreading in Europe. Seven polymorphic microsatellite loci were surveyed to characterize genetic structuring of D. v. virgifera populations, based on 595 individuals sampled from 10 locations across nine U.S. states (western Texas and Kansas to New York and Delaware). All populations showed high levels of genetic diversity, with mean allelic diversity ranging from 7.3 to 8.6, and mean expected heterozygosity ranging from 0.600 to 0.670. D. v. virgifera populations exhibited little genetic differentiation as a whole across the geographic range sampled, with a global F-ST of only 0.006. Pairwise F,, estimates also revealed little genetic differentiation among populations. Most pairwise Fs, values were nonsignificant, except for those estimated between the Texas population and all others. There was a positive correlation between genetic distance and geographic distance as a whole, but no significant correlation for populations from Kansas to the east coast. There was no evidence for a genetic bottleneck in any D. v. virgifera population sampled. Phylogenetic and principal component analyses support the picture of high genetic similarity over much of the United States. Although high migration rates could produce the same pattern and cannot be ruled out, it seems more likely that the D. v. virgifera populations sampled have had insufficient time for substantial genetic structuring to develop since its recent eastward range expansion from the Great Plains that began approximate to 50 yr ago.