Dr. Murai Éva szerk.: Parasitologia Hungarica 19. (Budapest, 1986)

nure were placed into plastics containers, together with a certain amount of manure, and transported by car to the site of testing. The test material collected in this manner was placed into a soil isolator near the laboratory. The hatched imagos were collected in a tulle isolator and transferred to the place of testing where they were fed on sugar, milk powder and water. This breeding method yields more flies, is more rapid and less labour- and materialintensive than laboratory breeding. Furthermore, flies obtained in this way are more representative of the natural population and the laboratory strains are not exposed to the risk of getting infected. For detailed descn ption of the method see the paper of SZABÓ and MÉNESI (1985, in press. As sensitive strain, the WHO/SRS strain (WHO, 19 65), regularly sent to us from Pavia, Italy, was used. The pupae were reared on YMA medium, consisting of yeast, milk powder, agar and water (SAWICKI, 19 64). The imagos were fed with granulated sugar and water, and in the period of ovulation also with milk. Breeding took place in a climatized chamber at a temperature of 26jT°C, at 60+5% relative humidity, and with a 16-h lighting period (150 lux). Insecticides The pp'-DDT (1, 1, l-trichloro-2, 2-bis(4-chlorophenyl)ethane) and gamma-HCH (1, 2, 3, 4, 5 (3, 6-hexachlorocyclohexane)) active substances of at least 99 % purity were purchased from the Riedel-de Haen Ltd. The active substances were dissolved in acetone of 95% purity. Fig. 1 Geographic distribution in Hungary of the 18 farms at which housefly populations were collected (for names of localities see the text)