Monitoring and molecular mechanisms of resistance to complex III inhibitors in Tetranychus urticae populations from Türkiye.

Acequinocyl and bifenazate are widely used acaricides that inhibit mitochondrial electron transport at complex III, due to their high efficacy and low side effects. However, resistance development has been reported in Tetranychus urticae populations worldwide, likely as a result of frequent applications. This study assessed the phenotypic resistance levels of T. urticae populations collected from commercial vegetable and ornamental greenhouses in Türkiye to complex III inhibitors. Most populations remained susceptible, although resistant populations were also identified and further characterized. Although previously known mutations were absent, we discovered a novel M128T mutation in a highly conserved region of the cd1 helix of the mitochondrially encoded cytochrome b in the populations exhibiting the highest levels of resistance to complex III inhibitors. Reciprocal crosses confirmed the maternal inheritance of moderate resistance to complex III inhibitors, thereby supporting the involvement of the novel mutation in conferring resistance. However, these crosses also revealed the presence of additional mechanisms contributing to the high resistance levels, as indicated by the mutation's moderate phenotypic effect. Transcriptomic analysis revealed the overexpression of multiple detoxification genes, particularly several P450 monooxygenases (P450s), in the resistant T. urticae population from Tu4S (LC > 10,000 mg a.i./L). Although the functional validation of these overexpressed genes is still required, our results indicate that a synergistic interaction between target-site and metabolic resistance mechanisms contributes to the high resistance levels.