Weekly releases of about 1600 ♀ pteromalid wasps,Pachycrepoideus vindemiae(Rondani), per m2eliminated populations of house flies,Musca domesticaL., stable flies,Stomoxys calcitrans(L.), andFanniaspp. at a poultry house after 98 days. Releases of 633 ♀/m2in a box stall which housed a Holstein steer reduced house fly populations about 40% after 28 days. A population model derived from the results of laboratory and field tests could be used to estimate wasp populations in colonies and to determine the population dynamics of the wasp in the field.