Influence of Selected Insecticides on the Population Dynamics of Diamondback Moth (Lepidoptera: Plutellidae) and Its Parasitoid, Diadegma insulare (Hymenoptera: Ichneumonidae), in Cabbage

The effects of insecticides on the diamondback moth, Plutella xylostella (L)., and its parasitoid, Diadegma insulare (Cresson), were evaluated in the field. Insecticides applied for control of the diamondback moth caused variations in parasitism by D. insulare ranging from 20 to 84%. Permethrin applications were effective at controlling diamondback moth. Applications of spinosad also resulted in low diamondback moth populations; however, percent parasitism was higher than in untreated plots and over 4× higher than in plots treated with permethrin. Selective materials that conserve D. insulare populations and maintain diamondback moth populations below economic thresholds may reduce the frequency of application, thus prolonging the efficacy of these materials.