Development of resistance to a mixture of spiromesifen and abamectin and cross resistance in Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae, a polyphagous pest, can feed on many plants. Farmers generally prefer chemical control to mitigate T. urticae, the arthropod species in which pesticide resistance is most common. In this study, resistance development to spiromesifen + abamectin mixture formulation, mixture formulation with active ingredients spiromesifen and abamectin, and cross resistance rates to spirodiclofen, milbemectin and spirodiclofen + abamectin were determined in the T. urticae strain selected for resistance to the spiromesifen + abamectin mixture. Spiromesifen+abamectin with LC50 and LC90 values for the susceptible T. urticae (GSS) strain were 0.53 mg a.i./l and 2.66 mg a.i./l distilled water, respectively. In the strain selected and named IR, the LC50 value increased to 640.50 mg a.i./l distilled water and the resistance ratio increased 1199-fold. The IR strain developed 1759 fold resistance to abamectin and 25 8874-fold resistance to spiromesifen, which is one of the active ingredients of the mixture. In cross-resistance studies, LC50 resistance ratios for spirodiclofen, milbemectin and spirodiclofen + abamectin were increased by 224-, 40-, and 1069-fold, respectively. The use of pesticide mixtures used to delay or prevent the development of resistance of pest species should be reconsidered.

Automated summary

This study investigated the resistance development of the two-spotted spider mite to various pesticides and suggested re-consideration of pesticide mixtures to address resistance issues in pest species.