First Report on Field-Evolved Resistance to Lambda-Cyhalothrin in Rice Leaf Folder (Cnaphalocrocis medinalis Guenee)...

Insecticide overuse in agriculture raises significant concerns, particularly in rice cultivation, where pest management heavily relies on chemical control. Major pests, such as rice leaf folders, are frequently targeted, leading to increased insecticide applications and subsequent selection pressure, fostering resistance development. Resistance in rice leaf folder, Cnaphalocrocis medinalis to diamide and organophosphate groups of insecticides has already been reported. However, despite the widespread use of synthetic pyrethroids, particularly lambda-cyhalothrin, in Kerala, India, data on resistance levels and underlying mechanisms remain sparse. This study bridges this gap by assessing the susceptibility of field populations of C. medinalis to lambda-cyhalothrin and investigating the key biochemical mechanisms driving resistance. Resistance ratios (RR) across populations were alarmingly high, ranging from 170.73- to 763.66-fold, indicating significant resistance. Biochemical assays revealed elevated detoxification enzyme activity, including CarE (1.11-1.63 times), GST (2.33-2.97 times), and Cyt P450 (1.52-2.49 times). Synergism assays confirmed metabolic resistance mechanisms, with increased CarE activity contributing to resistance in the PKD population, elevated Cyt P450 activity in the KUD and ONT populations, and multiple detoxification enzymes involved in resistance in the TCR population. This marks the first documented evidence of field-evolved resistance to lambda-cyhalothrin in C. medinalis globally. The outcomes highlight serious implications, as high resistance levels may prompt more frequent and higher doses of insecticide applications, increasing the risk of unintentional environmental contamination, particularly in aquatic ecosystems. Moreover, evidence from other lepidopteran pests suggests that chronic exposure to broad-spectrum insecticides may enhance preadaptive detoxification pathways, perpetuating a pesticide treadmill and accelerating resistance evolution. Given these findings, the study emphasizes the urgent need for resistance monitoring and integrated resistance management strategies to sustain rice productivity while mitigating ecological risks and preserving the long-term efficacy of available insecticides.