Abstract
Susceptibility to six pesticides of eight populations of the diamonback moth, Plutella xylostella, collected from Wakayama prefecture was determined in 3rd inster larvae by the leaf dipping method. Most of the populations showed remarkably reduced susceptibility to methomyl, prothiophos and acephate. Low susceptibility to fenvalerate + malathion was found in the populations collected from Wakayama, Gobou and Inami, where cruciferous crops were extensively grown in spring and autumn. Furthermore, the Gobou population showed low susceptibility to permethrin, cypermethrin and flucythrinate. All populations except the Gobou population were toxic to cartap. Although no resistance to Bacillus turingiensis (Toaro CT) was found among 6 populations, LC50 value against B. turingiensis in the Gobou population was higher than that of the other populations, and increased with time.
