Abstract
Thirty nine populations of the cotton aphid, Aphis gossypii GLOVER, collected in the field in Shizuoka Prefecture, Japan were tested for susceptibility to several insecticides and individual variation of esterase activity. When LC50 values of organophosphorus insecticides (OP), dichlorvos and malathion were compared, the aphids from melon, cucumber, watermelon, chrysanthemum and strawberry hosts exhibited higher resistance than the aphids from potato, eggplant, Hibiscus syriacus and Celastrus orbiculatus. These resistance levels were not always correlated to frequency of insecticide application. This showed that OP resistance of the aphid may be closely related to its host. A moderate resistance to carbaryl, a carbamate was observed. Fenvalerate, a pyrethroid, mixed with malathion was highly toxic to all aphids tested including OP-resistant ones. Aphid individuals with high esterase activity were observed frequently in OP resistant populations. Therefore LC50 value of OP was positively correlated with means of individual esterase activity.
