Gene Flow and Diversity at Allozyme Loci in the Twospotted Lady Beetle (Coleoptera: Coccinellidae)

Abstract

High levels of genetic variation in biological control agents are thought to be necessary to ensure their successful establishment and geographical spread. Gene diversity was studied in F2 twospotted lady beetle, Adalia bipunctata (L.), descended from specimens collected in Uzbekistan and from beetles collected in Oregon, Iowa, and Lake Michigan at Chicago, IL. Twenty-four of 39 resolved putative loci were polymorphic and the mean observed heterozygosity was 22.7 ± 4.4% at the polymorphic loci. The average expected heterozygosity was 24.7 ± 4.9% at the polymorphic loci and 15.2 ± 3.3% at all loci. The mean number of alleles at the 39 loci was 1.9 ± 1.0, and the mean effective number of alleles was 1.3 ± 0.5. These are substantial levels of diversity. Significant departures from random mating were detected within ( FIS = 0.068 ± 0.042) and among ( FST = 0.070 ± 0.012) the North American populations but matings were random within populations when problematic loci were excluded. Analysis of gene frequencies at 5 loci in 4 British and a French population showed the same magnitude of gene flow as the 3 North American populations. The fixation index between Iowa and Uzbekistan ladybirds was FST = 0.428 ± 0.128. Our data do not support an Old World origin for North American A. bipunctata in historical times.