Abstract
Susceptibility to several insecticides of housefly populations collected from hog and chicken farms as well as garbage dumping land-fill sites in Chiba-ken, Tochigi-ken, Ibaraki-ken and Tokyo was determined by the topical application method and compared with that of CSMA, a susceptible strain. A significant level of resmethrin resistance, i. e. 5.2μg/_??_ in LD50 and 179 fold in resistance factor, was detected only with the colony collected from the same hog farm in Mashiko, Tochigi-ken as where the first case of pyrethroid resistance was found in 1983. All other colonies were highly susceptible to resmethrin except one from the garbage dumping land-fill site of Yachiyo, Chiba-ken, which showed a slight decrease in susceptibility to the pyrethroid. All the colonies except CSMA strain were highly resistant to p, p′-DDT. The flies were also found retaining resistance reported in 1970s to organophosphorus insecticides such as diazinon and fenitrothion to varying degrees.
