none Microplitis croceipes; MELANISM-; GENOTYPE-; MUTATION-; COLOUR-VARIATION; Black abdomen mutant genetic characterization. A spontaneous abdomen color mutant, Bad, was observed in a parasitic wasp, Microplitis croceipes (Cresson). The inheritance pattern indicates that the abdomen color trait is controlled by a semidominant gene. Haploid males have normal yellow abdomen in the wild-type strain and the black abdomen in the mutant strain. The abdomen of the diploid females shows an intermediate color pattern when the locus is heterozygous. There is some evidence for the existence of a second gene locus that also influences color deposition.