The introduction of new exotic species of larval and pupal parasites (probably from the Eastern Hemisphere) and the artificial distribution of existing parasites appear to offer the most immediate means for a more successful biological control effort in southern California, especially against Musca domestica, the most common of the house flies. Existing parasites are, how-ever, not as effective against this species as they are against Fannia and certain other species.

This study was supported in part by grants from the National Institutes of Health, U. S. Public Health Service and from the California Department of Public Health Fly Control Research Project.