Toxicity of a novel acaricide, bisulflufen, to the two-spotted spider mite Tetranychus urticae.
BACKGROUND The two-spotted spider mite (TSSM), Tetranychus urticae, is a major global agricultural pest that has developed resistance to nearly all acaricides used for its control. This study evaluated the toxicity of bisulflufen, a novel phenyl trifluoroethyl thioether acaricide, against the TSSM. RESULTS Bisulflufen exhibited high toxicity across all developmental stages of the TSSM, with peak activity observed at 72 h post-application compared with 24 and 48 h. In a laboratory-maintained susceptible strain, the median lethal concentration (LC₅₀) values of bisulflufen at 48 h were 9.61 mg L-1 for female adults (determined as baseline susceptibility), 10.17 mg L-1 for nymphs, and 0.58 mg L-1 for eggs (based on hatch inhibition). Temperatures ranging from 15 to 30 °C did not significantly affect the toxicity of bisulflufen at 48 h. Seven field populations collected across China remained susceptible to bisulflufen (LC₅₀ = 7.34-13.67 mg L-1). However, these populations exhibited high levels of resistance to two commonly used acaricides, cyetpyrafen and bifenazate, with resistance ratios of 1260.5-4898.1-fold and 5.0-671.6-fold, respectively. Field trials demonstrated that 15% bisulflufen SC applied at 150, 100, and 75 mg L-1 effectively controlled the TSSM, achieving efficacies exceeding 99.09% 3 to 14 days post-treatment. CONCLUSION The baseline susceptibility of TSSM female adults to bisulflufen, established using a laboratory susceptible population, yielded an LC₅₀ of 9.61 mg L-1. Bisulflufen exhibits high intrinsic toxicity and excellent field efficacy against the TSSM, making it a promising tool for managing populations resistant to commonly used acaricides. © 2026 Society of Chemical Industry.