Insecticide Resistance Characteristics of Diamondback Moth

Resistance to organophosphorus, carbamate and pyrethroid insecticides in the diamondback moth, Plutella xylostella (L.) is widespread in Japan. Consequently, tertiary amines such as cartap and thiocyclam, microbial insecticides (formulations of Bacillus thuringiensis Berliner) and chitin synthesis inhibitors have been widely used for control. A high level of resistance to these alternative insecticides has been observed. Organophosphorus insecticide resistance gradually develops by insecticidal selection. The resistance is rather unstable, but i ts stability tends to increase with resistance levels. Cross-resistance to organophosphorus insecticides is related to chemical structure of insecticides. Development of pyrethroid resistance is extremely rapid in the field and is more stable than organophosphorus insecticide resistance. Pyrethroidresistant DBM exhibits high levels of resistance to various kinds of pyrethroids. A high level of resistance to tertiary amines and B. thuringiensis was induced in the field with successive applications, although development of the resistance is not fast. Tertiary amine resistance is more stable than B. thuringiensis resistance. Bacillus thuringiensis resistance decreased from a high to moderate level in a few generations in the absence of insecticide selection pressure during rearing.