Gene flow in populations of the seven-spotted lady beetle, Coccinella septempunctata

Polyacrylamide gel electrophoresis was used to reveal gene diversity in exotic North American Coccinella Septempunctata populations. This lady beetle recently spread across the northern Nearctic. Sixteen of 28 putative loci were polymorphic; average gene diversity for all loci was 0.1598 ± 0.041. Gene frequencies were estimated at eight polymorphic loci in natural North American beetles from Arkansas, Delaware, IA, Kansas, New York, Oregon, and Michigan. Also studied were F₂ beetles from four laboratory colonies that originated in Eurasia, along with field-collected beetles from France, Greece, and Sicily. Gene diversity among the Nearctic beetles was as great as that among the Palearctic beetles. Analysis of variance by Wright's method showed that only 29% of the variance in gene frequencies was between USDA cultures, Palearctic, and Nearctic beetles; 71% of the genetic variance was shared by beetles within the 21 subpopulations. No evidence of bottlenecks of drift was detected among the Nearctic subpopulations, and gene flow was essentially unrestricted.