Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2007
Publication Date: June 1, 2007
Citation: Kim, K.S., French, B.W., Sumerford, D.V., Sappington, T.W. 2007. Genetic Diversity in Laboratory Colonies of Western Corn Rootworm (Coleoptera: Chrysomelidae) including a Nondiapause Colony. Environmental Entomology. 36(3):637-645. Interpretive Summary: The western corn rootworm is the main pest of corn in North America and much of Europe. It is the subject of experiments in many laboratories to learn about its biology, ecology, behavior, and genetics. For many experiments, large numbers of rootworms are obtained from laboratory colonies maintained at the North Central Agricultural Research Laboratory (NCARL) in Brookings, SD. When insects are reared in the laboratory, sometimes they lose genetic variability due to purposeful or accidental selection, or by chance if the populations get too small. We examined variation in the DNA to determine how much variability has been lost in several laboratory colonies compared to rootworms captured from wild populations, and found that for the most part, wild and laboratory-reared insects are very similar genetically. An exception is the "nondiapause" line, which is popular because it was selected in the past to have a short generation time, making it convenient to use in many cases. This line has lost about one-fourth of the genetic diversity found in wild populations. Even so, this loss is much less than expected, and this line will continue to be of use in many studies. This information will help researchers who use these laboratory lines better design their experiments and interpret their results.
Technical Abstract: 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 this major insect pest. A non-diapausing line developed via artificial selection in the early 1970s is particularly attractive for many studies because its generation time is much shorter than that of typical diapausing colonies. However, the nondiapausing colony has been in culture for approximately 200 generations without out-crossing. We compared variation at six microsatellite loci among individuals from the NCARL nondiapausing line (~200 generations), main diapausing line (~22 generations), four regional diapausing lines (~7 generations), and four wild populations. Genetic diversity was very similar among the diapausing laboratory lines and wild populations. However, the nondiapausing line showed about 15-39% loss of diversity depending on the measure. Pairwise estimates of Fst's were very low, revealing little genetic differentiation among laboratory colonies and natural populations. The nondiapause line showed the greatest genetic differentiation with an average pairwise Fst of 0.153. There was little evidence that the laboratory lines had undergone genetic bottlenecks except for the nondiapausing line. Taken together, the results indicate that the diapausing colonies maintained at NCARL are genetically similar to wild populations. The nondiapause colony has suffered a moderate loss in genetic diversity and is somewhat differentiated from wild populations. This was not unexpected given its history of artificial selection for the nondiapause trait, and the large number of generations in culture.