ABSTRACT
Standard WHO test methods were used to determine the susceptibility of field population of housefly to four organophosphorus and two pyrethroid insecticides. Field population flies were collected from nine governorates [Giza, Fayoum, Suez, Behaira, Monoufia, Sharqia, Kafr El-Sheikh, Assiut and Aswan]. The results indicated that all tested insecticides were very effective on flies collected from Sharqia, Kafr El-Sheikh and Aswan, but there was an increased vigor tolerance among those collected from Kafr El-Sheikh for bioresmethrin and tolerance for diazinon in Aswan. In Assiut, flies exhibited a high sensitivity to diazinon, deltamethrin and bromophos, while malathion was the least effective adulticide. A resistance to malathion, diazinon, fenthion and bioresmethrin was noticed in varying degrees at all governorates. The highest average resistance ratio was recorded for malathion in Behaira [55.3 folds] and in Suez [26 folds]. Resistance was also more pronounced in Monoufia for diazinon [23.3 folds]. As for bioresmethrin, an apparent increase in the resistance ratio was detected in Suez [25 folds]. In Giza, the houseflies were resistant to fenthion [14.5 folds]. Regarding the difference between the six insecticides used, deltamethrin was the most potent one in all governorates