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In the parasitoid wasp Bracon sp. near hebetor, unfertilized eggs develop as 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 sex determination known as single-locus complementary sex determination (CSD). Under single-locus CSD, individuals that are heterozygous at the sex locus are female and individuals that are ho- mozygous or hemizygous are male. In B. hebetor (Say), a closely related species in which this mechanism of sex determination was 1st discovered, diploid males are sterile and usually do not survive. In this study, the survival of diploid males was confirmed in B. sp. near hebetor by the use of phenotypic and molecular markers. Females with a recessive light body color mutation (blonde) crossed with dark-bodied males produced families in which diploid males were identified through inheritance of the dominant dark-bodied allele from the father. Polymorphic RAPD-polymerase chain reaction (PCR) markers were used to confirm inheritance of paternal alleles in diploid males. In families that 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. serinopae (Cherian) and B. brevicornis Wesmael) diploid males survive at high rates. The differential survival rates of diploid males between closely related species of Bracon may indicate that the CSD system is not as evolutionarily conserved as has been presumed.