Mechanisms of resistance to three mite growth inhibitors ofTetranychus urticaein hops

Abstract

AbstractMite growth inhibitors (MGIs), such as etoxazole and hexythiazox, are valuable IPM tools forTetranychus urticaecontrol in hops due to their unique mode of action and selectivity. Hence, it is necessary to standardize bioassay methods to evaluate the efficacy of MGIs, monitor resistance, and identify mechanisms underlying MGI resistance in the field. Here, we developed a three-tiered approach for evaluating ovicidal toxicity of MGIs toT. urticae, which simulated different MGI exposure scenarios in the field. The most effective bioassay method was direct exposure ofT. urticaeeggs to MGIs. With this method, four field-collectedT. urticaepopulations showed low-to-moderate resistance to MGIs. Cross-resistance among MGIs and from MGIs to bifenazate and bifenthrin was detected. Besides target site insensitivity, enhanced cytochrome P450 and esterase activities also contribute to the MGI resistance in hop yard-collectedT. urticaepopulations. Low-to-moderate MGI resistance inT. urticaepopulations may be mediated by multiple mechanisms. Positive selection pressure on theI1017Fmutation is moderate in field-collectedT. urticaepopulations. Further studies are required to identify metabolic detoxification genes that confer resistance to MGIs for precise resistance monitoring.