Frequency-dependent mate selection or the advantage of the rare-type male has been described in the genus Drosophila by several investigators. As this phenomenon may serve in the maintenance of variation in a population, it is desirable to determine if it is more widespread. To that end, several inbred strains of the wasp, Mormoniella vitripennis, were chosen for study. Most of the mutant strains examined revealed no minority effect but instead, wild wasps discriminated against the mutants. However with the strain peachpurple and the wild-type, a minority advantage among males appeared to be operative. Mating tests were performed by direct observation using 20 wasps per trial. Equal sex ratios were maintained in all trials. Females of each type were equally frequent; whereas, the ratio of mutant to wild males was varied (5:5, 8:2, 2:8). Approximately 300 matings were scored for each frequency. Although mating discrimination was observed and wild males were slightly more successful at equal frequency, the wild males demonstrated a marked increase in relative mating success when in the minority. Mutant males also showed a significantly increased mating succes when their frequency was lowered.