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

Parasit, hung. 19. 1986 Insecticide resistance of houseflies (Musca dornestica L.) in Hungary. I. Resistance to organochlorine insecticides Dr. László SZABÓ Research Institute for Heavy Chemical Industries, Veszprém, Hungary "Insecticide resistance of houseflies (Musca dornestica L.) in Hungary. I.Resistance to organochlorine insecticides" - Szabó, L. - Parasit. hung., 19: 81-91.1986. ABSTRACT. The insecticide resistance of 18 local Musca dornestica populations was surveyed in Hungary between 1983 and 1985. Three to five days old female imagos hatched from larvae and pupae collected on 18 animal farms were examined by topical application of insecticides, and the results were evaluated by probit analysis (the WHO/SRS housefly was used as sensitive strain). None of the 17 populations tested for resistance to DDT had normal susceptibility (resistance indices calculated from the LDgg values were 180, 250-500, 500-1000, or above 1000 for 1, 5, 5 and 6 populations, respectively. Resistance to HCH was found to be rather low (RIs: only on one population did RI exceed 10, in 3 populations it was between 5 and 10, and for the remaining 10 populations below 5). The LD^Q and LDy

0 values of the sensitive WHO/SRS strain for DDT were much higher than suggested by hitherto published data. KEY WORDS. Susceptibility tests, Musca dornestica L. , local populations, Hungary, WHO/SRS strain, resistance to DDT and HCH. The housefly (

M use a dornestica L.

) belongs to insect species that rapidly develop a high level of resistance to insecticides applied to control them. Resistance to DDT, the first important synthetic organochlorine insecticide, was observed already in the first years of use (SACCA, 1947; WIESMANN, 1947). During the almost forty years that have elapsed since that time, the housefly developed resistance to almost all active substances and agents used all over the world. Considering the public-health and animal-health significance of the housefly and the importance of its control, a survey has been conducted to gel to know its resistance to insecticides in Hungary. Between 1983 and 1985 we examined 18 housefly populations and 9 insecticides in various parts of Hungary. Two of the agents were organochlorine insecticides, 3 organophosphorous insecticides, and 4 belonged to the group of pyrethroids. In the present paper the resistance of the housefly to the two most frequently used organochlorine insecticides, DDT and HCH, is reported. In Hungary, the use of organochlorine insecticides was prohibited in 1968 and they have not been used since. In spite of this fact, it is necessary to be aware of the level and incidence of resistance developed to them. As pointed out by numerous authors (SAWICKI, 1975; KEIDING, 1980) the type of resistance and the pattern of cross-resistance may vary by places and populations, depending on the type of insecticides used for control and on the genetic potential of the populations. To gain a deeper understanding of the present insecticide resistance of the housefly in Hungary and to control housefly populations more efficiently in the future, one has to know the resistance that has developed to the various agents used so far. This applies to DDT, since houseflies resistant to it are in certain cases cross-resistant to other agents, but first of all to pyrethroids. Three major genes are involved in the develop-