Parasitoids in the family Pteromalidae contains several important species that have been successfully used in biological control programs against house flies and other muscoid flies associated with dairy and poultry production. During routine colony maintenance of M. raptor Girault & Sanders at USDA- CMAVE lab in Gainesville, Florida, some red eye males were found. They were isolated and mated to virgin wild type females. Females of the F1 generation were also isolated to prevent mating with wild males. They were mated to red eye males. F2 generation produced red eye females, which were used to establish a pure red eye colony. The red eye color is transmitted as an autosomal recessive mutation. Experiments were designed to compare the fitness of the mutant to the wild type. Fitness parameter such as fecundity, survival, attack rate, sex ratio, and development time were found to be comparable with the wild type. A pure line of the mutant has been in colony for several years now. The mutant could be use to monitor spread of parasitoid releases and establishment in release programs and also as biological markers in experiments.