MOLECULAR ECOLOGY AND EVOLUTION Genetic Diversity in Laboratory Colonies of Western Corn Rootworm (Coleoptera: Chrysomelidae), Including a Nondiapause Colony

Laboratory-reared western corn rootworms, Diabrotica virgifera virgifera, from colonies maintained at the North Central Agricultural Research Laboratory (NCARL) in Brookings, SD, are used extensively by many researchers in studies of the biology, ecology, behavior, and genetics of thismajor insect pest.Anondiapause colonydeveloped throughartiÞcial selection in theearly 1970s is particularly attractive for many studies because its generation time is much shorter than that of typical diapause colonies. However, the nondiapause colony has been in culture for 190 generations without out-crossing. We compared variation at six microsatellite loci among individuals from the NCARL nondiapause colony ( 190 generations), main diapause colony ( 22 generations), four regional diapause colonies (3Ð8 generations), and four wild populations. Genetic diversity was very similar among the diapause laboratory colonies and wild populations. However, the nondiapause colony showed 15Ð39% loss of diversity depending on the measure. Pairwise estimates of FST were very low, revealing little genetic differentiation among laboratory colonies and natural populations. The nondiapause colony showed the greatest genetic differentiation with an average pairwise FST of 0.153.Therewas little evidence that the laboratory colonies hadundergonegenetic bottlenecks except for the nondiapause colony. The nondiapause colony has suffered amoderate loss in genetic diversity and is somewhat differentiated from wild populations. This was not unexpected given its history of artiÞcial selection for thenondiapause trait, and the largenumberof generations inculture. Incontrast, the results indicate that the diapause colonies maintained at NCARL are genetically similar to wild populations.