Resistance to organophosphorus insecticides in the SKA strain of houseflies (Musca domestica)

The response of a susceptible strain and the diazinon-selected strain of houseflies, the SKA, to 20 organophosphorus insecticides was measured by topical application and injection. The SKA strain was very resistant to diazinon, “ethyl chlorthion”, “chlorthion” and parathion, moderately resistant to five other insecticides and only slightly resistant to the remainder. It was more resistant to the diethoxy than dimethoxy compounds and was only very slightly resistant to malathion. The compounds, especially the phosphates, were more toxic when injected than when applied topically. Additions or substitutions in the phenyl ring of the parathion molecule resulted in compounds less toxic than parathion, particularly to susceptible flies RESP-6480