Enantioselective Bioactivity and Molecular Basis of Fluralaner Enantiomers in Tetranychus cinnabarinus (Boisduval)

Fluralaner, a chiral isoxazoline compound, exhibits pronounced enantioselective toxicity against Tetranychus cinnabarinus, a significant agricultural mite. In this study, the S-(+)-fluralaner enantiomer exhibited over 75-fold higher adulticidal activity and more than 225-fold stronger inhibition of egg hatching compared to the R-(−)-enantiomer. Enzymatic degradation assays indicated that the R-form was preferentially metabolized by mite enzymes. Transcriptomic profiling and biochemical validation identified cytochrome P450 monooxygenases as key contributors to this enantioselective detoxification. Electrophysiological recordings in Xenopus laevis oocytes expressing the GABA receptor subunit TcRDL2 revealed enantioselective inhibition of GABA induced currents, with S-(+)-fluralaner exhibiting the greatest antagonistic effect. Structural modeling further demonstrated distinct hydrogen bonding patterns between each enantiomer and TcRDL2, providing a mechanistic explanation for their differential activity. These results suggest that both metabolic and target selectivity contribute to the superior bioactivity of S-(+)-fluralaner, supporting its potential as a enantiomer-specific acaricide and informing the rational design of next-generation chiral pesticides.