Medical and Veterinary Entomology zyxwvu (1989) zyxwvu 3, 169-178 Influence of habitat and temperature on dispersal behaviour of two pteromalid parasitoids of houseflies during an inundative release at a dairy barn LINCOLN SMITH, DONALD A. RUTZ and GLEN A. SCOLES Department of Entomology, Cornell University, Ithaca, New York ABSTRACT. 1. About 11,000 each of Muscidifurux zyxw ruptor Girault and Saunders and Urolepis rufipes (Ashmead) were released weekly for 7 weeks at a commercial dairy farm in central New York state, U.S.A. Dispersal behaviour was monitored by parasitism rates of house fly, Muscu domesticu L., pupae placed in sentinel bags. 2. M.ruptor, which was released inside the barn, parasitized fly pupae both inside and outside, and it achieved highest rates of parasitism in indoor straw calf-bedding and in outdoor manure and silage. 3. U.rufipes, which was released outside the barn, did not attack pupae inside the barn, and its highest rates of parasitism occurred in outdoor manure and silage. zyxwv 4. M. ruptor appeared to be more effective than U. rufipes in parasitizing pupae located at sites where natural fly-breeding occurred. 5. Interspecific competition did not appear to explain these distribution patterns. 6. There was no significant trend in parasitism by M.raptor as a function of distance from the release station. Furthermore, high rates of parasitism near open doorways and at an outdoor site 30 m away suggests that M. ruptor dispersed throughout the barn and its immediate surroundings. 7. Air temperature was positively correlated to flight activity, but not to parasitization activity in natural fly-breeding substrates. Key words. Hymenoptera, Pteromalidae, microhabitat, livestock, para- sitoid, dispersal, biological control, behaviour, interspecific competition. zy Introduction The use of pteromalid parasitoids for biological control of filth flies has reached the stage where commercial insectaries are selling fly para- sitoids. Although some of the documented attempts to control flies by releasing these para- Correspondence: Dr Donald A. Rutz, Department of Entomology, Cornstock Hall, Cornell University, Ithaca, NY 14853, U.S.A. sitoids have been successful, many have failed, which indicates the need to understand more about the ecology, behaviour and population dynamics of these species (Meyer, 1986). Much emphasis has been placed on the importance of host specificity, foraging behaviour, phenology, and population dynamics in studying the effec- tiveness of parasitoids as biological control agents. However, an important area of research that has received relatively little attention is dis- 169