Bifenazate, a potent acaricide that targets mitochondrial
complex
III, exhibits selective toxicity (>280-fold) toward phytophagous
mites
versus predatory mites. Here, a systematic study was conducted to
clarify the selective mechanism. Nontarget factors were excluded through
epidermal penetration tests and assessment of detoxification enzymes’
activities. Quantification of IC50 values, ATP content,
and reactive oxygen species (ROS) levels revealed that differences
in drug-target binding determine the toxicity selectivity. Structural
modeling and molecular docking revealed that variations in key amino
acid sites within the cytochrome b (cytb) target
might regulate this selectivity, which was validated through a microscale
thermophoresis assay. Significant disparities were observed in the
binding affinity between bifenazate and recombinant cytb proteins
derived from phytophagous mites and predatory mites. Mutating isoleucine
139 to leucine notably reduced the binding affinity of bifenazate
to cytb. Insights into bifenazate selectivity between phytophagous
and predatory mites inform a basis for developing compounds that target
cytochrome b.