Survival of diploid males in Bracon sp. near hebetor (Hymenoptera : Braconidae)

In the parasitoid wasp Bracon sp. near hebetor; unfertilized eggs develop a s haploid males, but fertilized eggs are diploid and can develop into males or females. It is likely that the sex of diploid individuals is determined by allelic variation at a single sex locus within a system of seu determin ation known as single-locus complementary sex determination (CSD). Under si ngle-locus CSD, individuals that are heterozygous at the sex locus are fema le and individuals that are homozygous or hemizygous are male. In B. hebeto r (Say), a closely related species in which this mechanism of sex determina tion was 1st discovered, diploid males are sterile and usually do not survi ve. In this study, the survival of diploid males was confirmed in B so near hebetor by the use of phenotypic and molecular markers. Females with a rec essive light body color mutation (blonde) crossed with dark-bodied males pr oduced families in which diploid males were identified through inheritance of the dominant dark-bodied allele from the father. Polymorphic RAPD-polyme rase chain reaction (PCR) markers were used to confirm inheritance of pater nal alleles in diploid males. In families thai included diploid males, only 44% of diploids were male, indicating that diploid male survival is lower than female survival. Diploid males also are capable of mating, but mating by diploid males constrained females to producing only haploid male progeny . In the closely related species B. hebetor, diploid males rarely survive, but in other Bracon sp. (B scrinopae [Cherian] and B. brevicornis Wesmael) diploid males survive at high rates. The differential survival rates of dip loid males between closely related species of Bracon may indicate that the CSD system is not as evolutionarily conserved as has been presumed.