Fipronil, a broad-spectrum insecticide targeting Rdl-GABA receptors, is widely used in rice pest management. Although its environmental risks are well-documented, data on fipronil resistance in Cnaphalocrocis medinalis remain scarce. Investigating the metabolic and molecular mechanisms of resistance is essential for informed resistance management and sustainable use. Our study identified moderate-to-high fipronil resistance (11.67- to 154.83-fold) in rice leaf folder, Cnaphalocrocis medinalis, suggesting that repeated fipronil applications may exacerbate environmental risks. For the first time, we characterized the Rdl gene in C. medinalis, identifying a serine residue at position 282 in TM-2 across all tested populations, including the susceptible strain. Notably, the nonsynonymous mutation V457F in TM-4 was exclusively detected in the highly resistant TCR population, suggesting the potential role of target site insensitivity in this population. Metabolic resistance mediated by cytochrome P450 detoxification enzymes was confirmed in three populations (PKD, KUD, ONT) through synergism assays (SR = 2.35- to 4.57-fold). The novel V457F mutation in the conserved region of the Rdl receptor warrants further investigation in other fipronil-resistant insects. Cnaphalocrocis medinalis has developed moderate-to-high resistance to fipronil, with metabolic resistance confirmed in three of the study populations. Additionally, the potential involvement of Rdl-GABA receptor insensitivity was identified in the TCR population, which exhibited the highest resistance. © 2025 Society of Chemical Industry.
Subhagan et al. (Sat,) studied this question.