Enhanced metabolism associated with resistance to mite growth inhibitors in Tetranychus turkestani from Iran

Abstract

Spider mites are significant agricultural pests in apple orchards, where their control relies heavily on acaricide applications. In this study, seven populations of Tetranychus turkestani were collected from apple orchards in Isfahan Province, Iran, to evaluate their susceptibility to hexythiazox and etoxazole. Probit analysis revealed significant resistance to hexythiazox in T. turkestani populations, with resistance ratios (RRs) ranging from 290- to 2550-fold, while resistance to etoxazole was comparatively lower (RRs: 12- to 65-fold). Synergism assays revealed that a cytochrome P450 inhibitor significantly increased hexythiazox toxicity (up to 12-fold) and etoxazole toxicity (<3-fold) in the resistant populations. Inhibitors of carboxylesterases, ATP-binding cassette transporters and UDP-glucuronosyltransferases also significantly enhanced toxicity, while glutathione S-transferase inhibition had moderate effects. Enzyme assays indicated significantly higher P450 activity in some resistant T. turkestani populations. Screening the target-site chitin synthase 1 (CHS-1) revealed that the I1017F mutation, associated with the resistance in T. urticae, was absent in all T. turkestani populations. This suggests that the observed resistance in T. turkestani populations is primarily driven by increased metabolism. In contrast, this mutation was fixed in a T. urticae population, collected from greenhouse cucumbers, with extremely high LC₅₀ values to both acaricides. This study highlights the roles of detoxification enzymes in T. turkestani resistance to hexythiazox and etoxazole and underscores the need for further research into specific detoxification genes contributing to resistance.