Effects of encapsulation on the toxicity of insecticides to the Oriental fruit moth (Lepidoptera: Tortricidae) and the predator<i>Typhlodromus pyri</i>(Acari: Phytoseiidae)

Abstract

Abstract We assessed the effects of microencapsulation on the toxicity of chlorpyrifos, cypermethrin, and lambda-cyhalothrin to larvae of the Oriental fruit moth, Grapholita molesta (Busck), in the laboratory and the field. We also compared the toxicity of microencapsulated and traditional formulations to pyrethroid-susceptible and pyrethroid-resistant populations of the predaceous mite Typhlodromus pyri Scheuten in the laboratory. In laboratory bioassays with neonate larvae of G . molesta , the microencapsulated formulations of chlorpyrifos and cypermethrin were less toxic than the wettable-powder and emulsifiable-concentrate formulations. The emulsifiable-concentrate and microencapsulated formulations of lambda-cyhalothrin were equally toxic. In the field, all trees in insecticide-treated plots contained less damage by first generation G . molesta larvae than unsprayed controls. In the second generation, the microencapsulated formulations of cypermethrin and chlorpyrifos were generally less effective than the emulsifiable-concentrate formulation of cypermethrin. The microencapsulated formulation of lambda-cyhalothrin was as effective as the emulsifiable-concentrate formulation. The microencapsulated formulation of cypermethrin was less toxic than the emulsifiable-concentrate formulation to both pyrethroid-susceptible and pyrethroid-resistant populations of T . pyri . Both populations were highly resistant to chlorpyrifos and unaffected by either formulation. The microencapsulated formulation of lambda-cyhalothrin affected the two populations of T . pyri differently; the microencapsulated formulation was approximately fivefold more toxic than the emulsifiable-concentrate formulation to the pyrethroid-susceptible population, but sixfold less toxic than the emulsifiable-concentrate formulation to the pyrethroid-resistant population. Much of the selectivity reported for the microencapsulated formulations of cypermethrin and chlorpyrifos appeared related to a general reduction in toxicity to both target insects and beneficial mites. The microencapsulated lambda-cyhalothrin was as toxic as the emulsifiable-concentrate formulation to the target insect but was less toxic than the emulsifiable concentrate to pyrethroid-resistant predator mites. This limited increased selectivity may be useful where resistant populations of predators occur.