Abstract
A pyrethroid resistant colony of the housefly collected from a hog farm in Mashiko was further selected with resmethrin for 10 generations in laboratory, and its LD50 values for various insecticides were determined in comparison with those of a susceptible strain. The flies selected showed cross resistance to all the synthetic as well as natural pyrethroids tested. The flies were also highly resistant to the organochlorine insecticide p, p′-DDT, implying the involvement of a common mechanism of resistance for both types of insecticides, i. e. decreased nerve sensitivity due to the gene kdr. Resistance to the other organochlorine insecticide γ-BHC, however, was nominal. In general the flies showed a moderate level of resistance to organophosphorus insecticides, while their resistance to propoxur, a carbamate, was fairly high.
