Abstract
The local variabilities of resistance to malathion and methyl parathion were studied with green rice leafhopper colonies collected from various areas in Kanto, Chugoku and Shikoku districts of Japan. Low level of resistance to malathion was found in some colonies of Tochigi, Yamaguchi, Kochi, Ehime, Kagawa and Tokushima Prefectures. While, to methyl parathion low levels of resistance were found in some colonies of Kochi, Ehime, Kagawa, Tokushima, Okayama, Hiroshima and Shimane Prefectures. Close relationship was obtained between the levels of resistance in the leafhoppers to malathion and amounts of malathion previously applied in paddy field. But other organophosphorus insecticides might have more or less relations to malathion resistance. Levels of resistance of leafhoppers to methyl parathion were considered to depend on total amounts of organophosphorus insecticides (including methyl parathion) rather than methyl parathion only.
