Abstract
During a period of June and July, 1965, there was a great outbreak of housefly in the dump site, Yumenoshima Island, Tokyo. An enormous number of these flies supposingly moved to shopping districts and became a great annoyance. On topical application, these flies taken from "Yumenoshima" proved to be highly resistant not only to DDT and γ-BHC, but also to organophosphorus insecticides such as malathion and diazinon. On the other hand, they showed only slight crossresistance against the other organophosphorus insecticides, DDVP, Baytex (fenthion) and Sumithion (fenitrothion). The larvae of the same colony were also resistant to malathion, but still susceptible to Baytex, Sumithion and DDVP.
