Diversity of sex-determining alleles in Bracon hebetor

In many hymenopterans, sex is determined at a single polymorphic 'sex locus '. Individuals that are heterozygous at this locus develop as females where as homozygotes and hemizygotes develop as diploid and haploid males, respec tively. Diploid males are developmentally inviable or sterile, and the like lihood of diploid male production depends in large part on allelic diversit y at the sex locus. We assessed sex allele diversity within and among five U.S. populations of the parasitoid wasp Bracon hebetor using a series of cr osses between isofemale lines. The study included two laboratory population s originating in Wisconsin, two field populations originating in Kansas and California, and a population purchased from a commercial insectary. Given the number of isofemale lines that we established, the maximum number of al leles that we could detect per population was 10. The number of sex alleles identified within populations ranged between three or four (for the two Wi sconsin populations) and nine (for the California population). Subsampling three or four alleles from each population for between-population crosses l ed to identification of 12 alleles. Of these, four were unique to the Calif ornia population, three were unique to one other population each, and one w as found in only two populations. Extrapolation of the relationships betwee n the subsampled lines led to a total estimate of 20 alleles within our lin es. The relatively high allele diversity in the field and commercial insect ary populations suggests that the sex determination load is relatively low in B. hebetor, and the differences in allele profiles between populations s uggest that interpopulation dispersal can increase sex allele diversity wit hin populations.