Cytochrome P450 CYP6CY3 Mediated Cross-Resistance to Isocycloseram and Fluralaner in Myzus persicae

The green peach aphid (Myzus persicae, Hemiptera: Aphididae) is a globally important pest. Isocycloseram (a novel isooxazoline) and fluralaner (a benzamide/sulfonamide) are novel insecticides. A Hainan-resistant population (HNR), exhibited 459- and 316-fold resistance to isocycloseram and fluralaner, respectively, compared with a Yunnan susceptible population (YNS). Synergist bioassays and enzyme activity analyses indicated that enhanced cytochrome P450 monooxygenase activity contributed to resistance. Transcriptomic and qRT-PCR analyses revealed that CYP6CY3 was upregulated 16.4- and 10.8-fold in HNR compared with YNS. RNA interference of CYP6CY3 significantly restored susceptibility to both insecticides. In vitro recombinant enzyme assays confirmed CYP6CY3-mediated metabolism of isocycloseram and fluralaner, and gene copy number analysis demonstrated a 7.09-fold amplification. These results reveal CYP6CY3-mediated cross-resistance to isocycloseram and fluralaner, representing the first mechanistic evidence of isoxazoline resistance in M. persicae.