DIFFERENTIAL TOXICITY OF PESTICIDES TO DIADEGMA-INSULARE (HYMENOPTERA, ICHNEUMONIDAE) AND ITS HOST, THE DIAMONDBACK MOTH (LEPIDOPTERA, PLUTELLIDAE)

Laboratory studies were done to evaluate differential toxicity of pesticides to adult Diadegma insulare (Cresson) and its host, the diamondback moth, Plutella xylostella (L.). Leaf-dip and direct-dip bioassays (diamondback moth larvae) and residual (adult diamondback moth and D. insulare) bioassays were used. None of the pesticides caused 100% mortality to diamondback moth larvae or adults at 1.0 mg (AI)/ml concentrations (except Bacillus thuringiensis var. kurstaki and esfenvalerate on larvae and adults, respectively). However, at 1.0 mg (AI)/ml, all insecticides except B. thuringiensis kurstaki were extremely toxic to D. insulare within 30 min after treatment. Chlorothalonil was not toxic to diamondback moth larvae or adults or to D. insulare at concentrations tested. Methomyl was the least toxic insecticide to diamondback moth larvae and adults, but caused 100% mortality of D. insulare 24 h after the insects were exposed (1.0 mg [AI]/ml). An integrated approach for control of diamondback moth with B. thuringiensis and D. insulare might permit control of diamondback moth without directly affecting D. insulare. The use of chlorothalonil for controlling crop diseases is compatible with management of diamondback moth because this fungicide does not affect D. insulare. However, it may affect entomopathogenic fungi that attack diamondback moth larvae or adults in the field.