The rice leaf folder, Cnaphalocrocis medinalis, is a major pest causing substantial yield losses in key rice-producing states of India, including Kerala. Despite widespread insecticide use, there is a lack of comprehensive data on the susceptibility of C. medinalis populations to commonly used insecticides in the region. This study evaluates the susceptibility status ofC. medinalis to ten commonly used insecticides across five major rice-growing agroecological units in Kerala: AEU 23(Palakkad Eastern Plains), AEU 4 (Kuttanad), AEU 3 (Onattukara Sandy Plains), AEU 6 (Kole Lands), and AEU 20(Wayanad Central Plateau). Bioassay results indicated that the population from Wayanad remained susceptible to all testedinsecticides, while other field populations exhibited high resistance to quinalphos (133.24-fold to 611.37-fold) and lambda-cyhalothrin (170.73-fold to 763.66-fold). Moderate to high resistance was observed against carbosulfan (25.40-fold to347.96-fold), chlorantraniliprole (71.75-fold to 1089.63-fold), and flubendiamide (67.91-fold to 1572.64-fold). Correlogramanalysis highlighted acephate as a viable option for management, as it showed no cross-resistance with other insecticides.Cartap and emamectin benzoate were detected as potential alternatives for managing diamide-resistant populations. Thehigh resistance to quinalphos and carbosulfan, and their correlation with multiple insecticides, indicate the need to temporarily discontinue their use for C. medinalis management in Kerala. This study provides the first comprehensive assessment of insecticide resistance in C. medinalis populations in Kerala and establishes crucial LC50 benchmarks for future resistance monitoring and management strategies.
Subhagan et al. (Mon,) studied this question.