Extensive monitoring of acaricide resistance and resistance mechanisms in Tetranychus urticae populations collected from strawberry production areas in Türkiye

Tetranychus urticae Koch (Acari: Tetranychidae) is a major pest of many crops, including strawberries. Its remarkable ability to develop resistance often leads to control failures under field conditions. In this study, phenotypic resistance levels of T. urticae populations—collected mainly from strawberries and a few from other crops—were evaluated against four widely used acaricides: etoxazole, abamectin, pyridaben, and bifenazate. Many field populations exhibited moderate to high resistance levels to the tested acaricides (exceeding 5000-fold in the case of etoxazole), indicating a loss of efficacy likely driven by intense selection pressure from frequent chemical use. Synergism assays suggested involvement of elevated detoxification enzyme activity, with the most pronounced synergism (up to 62-fold) observed for pyridaben following treatment with PBO, a cytochrome P450 inhibitor. Molecular screening revealed the presence of known target-site mutations: I1017F in chitin synthase I, I321T in GluCl3, H92R in the PSST subunit of complex I, and A269V in cytochrome b . Among these, the I1017F mutation was fixed in all populations except one, consistent with toxicity assay results showing over 5000-fold resistance to etoxazole in most populations. These findings highlight the dwindling number of effective chemical control options in strawberry production and underscore the urgent need for evidence-based resistance management strategies to ensure sustainable acaricide use. • Monitoring of acaricide resistance revealed the development of multi-resistance in Tetranychus urticae populations. • Bifenazate was the most effective acaricide against spider mites collected from strawberry crops. • The role of detoxification enzymes in acaricide resistance was demonstrated through synergism assays. • The I1017F mutation in chitin synthase I was fixed in almost all populations. • The I321T (GluCl3) and H92R (PSST) mutations were found to be segregating in several populations.