Abstract
In autumn of 1960, the failure of house fly control occurred after residual applications of diazinon in several districts in Ibaraki Prefecture. The following experiments were carried out in laboratory concerning to the resistance of house fly to diazinon or to the other organophosphorus insecticides. 1) By the contact test using filter papers on which diazinon emulsions were applied, the KT 50's of four strains from these districts were 5 to 8 times longer than that of susceptible Takatsuki strain. 2) By the topical application test, the LD 50's of diazinon to these four strains were 15 to 25 times higher than that of Takatsuki strain, thougth only 2 to 3 times resistant or tolerant to malathion and DDVP. 3) The wire-netting method, bringing the flies into contact to residues of diazinon emulsion in wire-netting petri dishes, were proved to be suitable and available for distinguishing resistant strains from susceptible one. 4) The F_1 strains which crossed the resistant strain to susceptible one were intermediately resistant to diazinon and the F_2 slightly decreased the resistance comparing to F_1 strains.
