Technical Abstract: This is a summary of an invited talk given at the IOBC workshop on Arthropod Mass rearing and Quality Control in Montpellier, France, in September of 2003. Quality control of mass-reared biocontrol agents for flies begins with the economical production of house flies. Flies can be produced for about 50 cents per batch of 10,000 fly pupae. Rearing parasitic wasps requires selection of wasps with good performance and production characteristics. Once the species has been selection, attention must be paid to maintaining host:wasp ratios that result in uniform rates of rates. Wasp colonies must also be monitored for disease and other problems that arise under mass-rearing conditions.