Organophosphorus insecticide susceptibility or the diamondback moth has been examined in various areas of Shimane Prefecture since 1980. The first incidence of high resistance to organophosphorus insecticides was observed in Yokota, where cruciferous crops had been grown on a large scale under frequent applications of insecticides. The occurrences of high resistance to fenvalerate have been observed in various fields in Shimane Pref. since 1985, which was only two years after the introduction of this insecticide. Susceptibility to various insecticides depends heavily on their application frequencies. A decline trend in susceptibility to tertiary amine cartap and BT was still moderate as of 1992.