Non-target effects of pesticides on adult Stethorus pusillus (Coleoptera: Coccinellidae)

Stethorus pusillus (Herbst) is a specialist predator of spider mites and is a key component of mite biological control in many cropping systems. In the Pacific Northwest (United States), S. pusillus is an established, introduced species that is commonly found in crops as a resident predator, but it is also released for augmentative biological control. Non-target effects of some insecticides and fungicides can disrupt biological control by S. pusillus, reducing its efficacy. In laboratory assays, we evaluated the susceptibility of S. pusillus to 25 different commercially available pesticides, including 4 fungicides and 21 insecticides/miticides, spanning 14 known modes of action. We assessed the effect of direct contact exposure on adult mortality of both diapausing and non-diapausing S. pusillus. We also evaluated the non-diapausing adults for sublethal effects (locomotion and predation). Broad-spectrum insecticides, including acetamiprid, thiamethoxam, abamectin, fenpyroximate, and cyantraniliprole, caused moderate to high mortality, while selective miticides, such as clofentezine, hexythiazox, acequinocyl, bifenazate, spirodiclofen, and cyflumetofen, were largely harmless to both diapausing and non-diapausing adults. Among the fungicides tested, copper hydroxide caused high mortality, while mancozeb, captan, and fluopyram + trifloxystrobin had no effects. These results provide a useful update on the pesticide susceptibility of this important predator, which can be used by growers to make judicious spray decisions.