Abstract
The development of resistance of houseflies to organophosphorus compounds at the dumping-islands in the Tokyo Bay has been reported by the present author since 1966. In the 3rd "Yumenoshima" where full coverage of OP spray is being performed daily, an enormous number of single fly species, Musca domestica vicina, has been established. The LD 50 values of flies collected from the 3rd "Yumenoshima" in June, 1974 were correlated to those of the 15th dumping-island colony in 1973. In September, 1974,a remarkably increased OP resistance was found, with the LD 50 values of 5.21 microgram for diazinon, 54.9 microgam for fenitrothion, 9.62 microgram for fenthion and 0.581 microgram for dichlorvos. On the other hand, they were still susceptible to pyrethroids.
