Gene flow and diversity at allozyme loci in the twospotted lady beetle (Coleoptera: Coccinellidae)

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 rwospotted 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 ± 49% 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 (F_IS = 0.068 ± 0.042 and among (F_ST = 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 F_ST = 0.428 ± 0.128. Our data do not support an Old World origin for North American A. bipunctata in historical times.