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

resistance to Pyrethrins synergized with piperonyl butoxide. The highest resistance was observed for populations (about 1/3 of the populations tested) in which permethrin had been used as a means of control. A few years later the survey was repeated by CHAPMAN (1984) who found that resistance to synergized Pyrethrine had not changed essentially, but 90 % of the populations tested had developed high resistance to permethrin. In the region of Harpenden, SAWICKI et al. (1981) ran screening tests to assess the resistance of houseflies to permethrin, bioresmethrin and Pyrethrins. Only a few populations exhibited resistance to permethrin (this resistance was not mediated by the kdr gene). In England, NICHOLSON and SAWICKI (1982) observed moderate resistance to permethrin and other synergized pyrethroids in one housefly population. Genetic studies have revealed that no kdr or superkdr resistance mechanism was involved in the development of that resistance. For a housefly population collected at a pig farm, CHAPMAN (1985) established 141-fold and 96-fold resistance to permethrin and deltamethrin, respectively. In Georgia (USA), where permethrin had been used in housefly control for two years, HINKLE, SHEPPARD and IVOLAN (1985) established a more than 100-fold permethrin resistance in a housefly population. In their extensive field trials conducted in Czechoslovakia with permethrin and deltamethrin, RUPES et al. (1981) found satisfactory efficacy: only two populations, in which these compounds had been applied earlier, were found to possess reduced sensitivity. Only one housefly population exhibited high (100-fold) resistance to both tetramethrin and permethrin (RUPES et al., 1982, 1983) which was attributed to cross-resistance between DDT and pyrethroids. This was the second Czechoslovakian report on kdr resistance in housefly. Such resistance was first observed in 1961 (RUPES and PINTEROVA, 1976) when DDT resistance could not be abolished by use of an F-DMC synergist. In Japan, the development of high pyrethroid resistance was not observed until quite recently, not even in housefly populations that possessed extremely high multi-resistance even by international standards (KUDAMATSU, HAYASHI and KANO, 1983). MOTOYAMA (1984) was the first who described a population characterized by very high resistance to all pyrethroids including permethrin. The resistance level dropped significantly upon pretreatment with piperonyl butoxide, indicating that resistance had developed through enhanced detoxification. All of the papers mentioned above furnish evidence on the pyrethroid, first of all permethrin, resistance of field housefly populations. The artificial selection, genetic and biochemical investigations performed in laboratories (SAWICKI, 1973; FARNHAM, 1977; DeVRIES and GEORGHIOU, 1981; CHANG and PLAPP, 1983; SCOTT, SHONO and • GEORGHIOU, 1984; GOLENDA and FORGASH, 1985) also suggest that the development of pyrethroid resistance poses a real hazard for the future, especially as concerns the long-acting, photostable pyrethroids. Using bioresmethrin, DeVRIES et al. (1980) selected a housefly population multiresistant to organophosphates and achieved 80-fold resistance. Testing that population against several pyrethroids, he found that a cross-resistance of varying degree had developed to 16 of them. SCOTT and GEORGHIOU (1985) subjected a field housefly population, which had earlier been exposed to occasional permethrin treatments for four years, to laboratory selection with permethrin over 22 generations and achieved an almost 6000-fold resistance. In Hungary, SZABÓ (1984, 1984a) monitored two housefly populations for permethrin and tetramethrin resistance in 1983, and found nearly 10-fold and more than 100-fold resistance, respectively. These two housefly populations were collected at chicken farms where synergized Pyrethrins had been used earlier. Formerly Pyrethrins had been used only occasionally in Hungary. The use of photostable pyrethroids dates back to the early 'eighties, when they were introduced into practice in a few places. Thus, the survey made by us in the years 1983 through 1985 can be considered a determination of the baseline resistance level which will be a good starting point in future investigations into the development of pyrethroid resistance. In populations that have already developed resistance, the underlying causes must be examined. These may include the earlier occasional use of pyrethroids, and possibly a DDT-pyrethroid cross-resistance. Especially the latter phenomenon must be examined in detail in the future.