Insecticide resistance in Musca domestica L. from Eastern England

Strains of houseflies were obtained from a refuse tip and 34 farms selected at random from Eastern England in 1984. Resistance was assessed to four insecticides that had been in use for fly control in the UK. Dose-response data were obtained by topical application of the insecticides and, in addition, a resistance test method was used in which flies were allowed to feed on sugar coated with either methomyl or azamethiphos. For both methods, the knock-down (KD) after 48 h was used as a measure of response. The ranges of resistance factors for the topical application method were, for methomyl, 1·1–15·9 at KD₅₀ and 2·1–17·0 at KD₉₅; for azamethiphos, 2·2–36·9 at KD₅₀ and 4·5–88·2 at KD₉₅; for pyrethrins + piperonyl butoxide, 0·9–6·8 at KD₅₀ and 1·4–13·4 at KD₉₅; and for permethrin, 1·7–34·8 at KD₅₀ and 2·2–112·5 at KD₉₅. The ranges of the resistance factors for the feeding tests were, for methomyl, 2·1–39·8 at KD₅₀ and 2·4–64·0 at KD₉₅, and, for azamethiphos, 5·6–51·7 at KD₅₀ and 8·8–92·0 at KD₉₅.