In the course of breeding from an original pair of N. nigroscutum, diploid ♀ ♀ (2n = 14), in addition to haploid ♀ ♀ (n = 7), were found by weighing the fourth generation of offspring. Diploid ♀ ♀ occurred only among the progeny of mated ♂ ♂, the progeny of virgins consisting solely of haploid ♀ ♀. Diploid ♀ ♀ are usually 20–30% heavier than their haploid brothers and are produced at the expense of sisters. The haploid ♀ ♀ mated readily but only 1 diploid ♀ out of 150 achieved successful copulation, as shown by the production of ♂ ♂. The ♂ ♂ produced were triploid (3n = 21} and as expected proved highly sterile. Although diploid ♀ ♀ have been known for about 45 years in some of the higher Apocrita, this is the first time they have been recorded in the primitive Symphyta. Pedigree analysis shows that the founding parents carried three complementary sex alleles, a, b, and c. Biparental heterozygotes, a/b, a/c, b/c, are ♂ ♂; biparental homozygotes, a/a, b/b, c/c, diploid ♀ ♀; and impaternate hemizygotes, a, b, c, haploid ♀ ♀.