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ABSTRACT To evaluate population‐specific susceptibility to pyrethroid insecticides, four field populations of Frankliniella intonsa collected from alfalfa fields in Inner Mongolia were assessed using ingestion and contact bioassays. Four pyrethroids—bifenthrin, cyfluthrin, cypermethrin, and deltamethrin—were tested. In ingestion assays, cypermethrin LC 50 values ranged from 3.00 to 20.42 mg/L, corresponding to resistance ratios of up to 6.81‐fold among populations. In contrast, contact bioassays revealed substantially greater variability, with bifenthrin resistance reaching 75.50‐fold in the HHG population. Synergistic bioassays showed generally low synergistic ratios (< 2), indicating limited involvement of metabolic detoxification, although a moderate effect of piperonyl butoxide (SR = 2.08) was observed in HHG. Among detoxification‐related genes, CYP12A4 expression in HHG was 4.6–8.8‐fold higher than in other populations. This overexpression suggests a potential but minor contribution of cytochrome P450‐mediated detoxification. Sanger sequencing of the voltage‐gated sodium channel (VGSC) gene identified the T929I mutation in all four populations, with resistant allele frequencies ranging from 26.2% to 50.0%. A strong positive correlation ( r = 0.93) was observed between Ile929 allele frequency and cypermethrin resistance levels, although this relationship was not statistically significant ( p = 0.07). These results suggest that the T929I mutation is likely associated with pyrethroid resistance in F. intonsa , whereas metabolic detoxification plays a limited and population‐dependent role. These findings provide a scientific basis for resistance monitoring and rational insecticide management in F. intonsa .
Gao et al. (Thu,) studied this question.