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

MATERIALS AND METHODS Characterisation of housefly strains, description of toxicity test and statistical evaluation of data are the same as in the 1 and 2 part (p. 81-91), High doses of tetramethrin (in populations 3 and 4) were administered in 2 or 3 fractions. Insecticides The following insecticides were used: - tetramethrin (cyclohex-1-ene-1, 2-dicarboximidomethyl (1RS)- eis - trans - 2,2 -dimethyls' (2-methylprop- 1-enyl) cyclopropanecarboxylate), obtained from the CHINOIN Pharmaceutical and Chemical Works Ltd. Purity: 97. 1%, cis/trans ratio: 34. 8/62. 3. - Cypermethrin ((RS)- oC-cyano-3-phenoxybenzyl (lRS)-cis-trans-3-(2, 2-dichlorovinyl)-2, 2dimethyl cyclopropanecarboxylate), obtained from the CHINOIN Pharmaceutical and Chemical Works Ltd. Purity: 99%. - permethrin (3-phenoxybenzyl (lRS)-cis-trans-3-(2, 2-dichlorovinyl)-2, 2-dimethylcyclopropanecarboxylate). A product of Riedel-de Haen Ltd. , a eis-trans isomer mixture. - deltamethrin ((S)- ot-cyano-3-phenoxybenzyl (lR)-cis-3-(2, 2-dibromovinyl)-2, 2-dimethylcyclopropanecarboxylate). A product of Riedel-de Haen Ltd. Purity: 99%. RESULTS Data on the sensitive strain The pyrethroid efficacy data of the WHO/SRS housefly, a strain that served for comparison, were more homogeneous and showed lesser deviation than those found for some organochlorine and organophosphate insecticides. Tetramethrin efficacy values are given in Table 1. The average LDgg, calculated on the basis of 10 experiments, was 0. 5782 jig/female. Cypermethrin efficacy values are indicated in Table 2. The most homogeneous values were obtained for this compound. The average LD

50 (calculated from 10 experiments) was 0. 0303 jjg/female. Permethrin efficacy values are shown inTable 3: of the four compounds tested, the least homogeneous results were obtained for permethrin. The average LDgn value (calculated from 10 experiments) was 0. 0646 jug/female. Deltamethrin efficacy values are shown in Table 4. Here the average LDgg (calculated from 5 experiments) was 0.0015 jag/female. This compound had the lowest regression coefficient (1. 88). Data on the populations tested Tetramethrin sensitivity data obtained for the populations tested are contained in Table 5. The resistance index calculated from the LD50 values was higher than 100, higher than 10, between 5 and 10, between 1 and 5, and below 1 in 2, 1, 2, 7 and 3 of the 15 housefly populations tested for tetramethrin sensitivity. Strikingly high resistance was found for populations no. 3 and 4, especially if the resistance index calculated from the LD95 values was taken into consideration. Population no. 5 also deserves attention: here the resistance index calculated from the LD^Q values hardly exceeded 10 but that derived from the LDQCJ values was much higher, indicating that the selection of specimens with a high resistance level had started. This is clear from the probit-regression lines of the sensitive strain and those of the field populations, shown in Fig. 1 . The figure also indicates that the tetramethrin sensitivity of several housefly populations is lower than that of the WHO/SRS strain. Cypermethrin sensitivity data are given in Table 6, Of the four compounds tested, Cypermethrin is the one to which the housefly populations are most susceptible. From Fig. 2 it is clear that several populations are more susceptible to Cypermethrin than the WHO/SRS strain. The resistance index calculated from the LD^Q values is higher than 5, between 1 and 5 and lower than 1 in 2, 6 and 7 populations, respectively. Population no. 5, having a moderate resistance to tetramethrin, is remarkable.