The 3 main spp. of flies inhabiting carrion in S. Africa are Lucilia sericata, Chrysomyia chloropyga, and C. albiceps. The majority of Lucilia larvae pupate in situations which are inaccessible to the parasite, whereas the 2 spp. of Chrysomyia have a large proportion of their pupal populations exposed to attack by the parasite. Results of expts. showed approx. percentages of exposure to attack by M. vitripennis as follows: L. sericata, 14; C. chloropyga, 50; C. albiceps, 77.