Lethal and sublethal effects of synthetic insecticides on feeding and nutritional physiology of Spodoptera frugiperda larvae

Abstract

Fall armyworm, Spodoptera frugiperda, is a major pest of maize, and insecticide-induced effects on larval feeding and nutritional physiology are important considerations for its management. The present study evaluated the lethal and sublethal effects of chlorantraniliprole + thiamethoxam, chlorantraniliprole, flubendiamide, and spirotetramat against 3rd- and 4th-instar S. frugiperda larvae under laboratory conditions. Each insecticide was tested at 5, 10, and 15 ppm, corresponding to 25, 50, and 100% of the recommended dose, respectively. Larval mortality, consumption index (CI), growth rate (GR), efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD), and approximate digestibility index (ADI) were assessed after 48 h. All insecticides and concentrations significantly affected larval mortality, with mortality generally increasing with concentration. Chlorantraniliprole + thiamethoxam was the most effective treatment, causing 97.96% and 88.51% mortality in 3rd- and 4th-instar larvae, respectively, at 15 ppm, whereas spirotetramat produced the lowest mortality (63.87% and 38.15%, respectively). Insecticide exposure also significantly reduced feeding and growth, with chlorantraniliprole + thiamethoxam generally producing the lowest CI and GR. ECI, ECD, and ADI were significantly lower in treated larvae than in the control, particularly following chlorantraniliprole + thiamethoxam exposure. Third-instar larvae generally exhibited greater susceptibility than 4th-instar larvae. Overall, chlorantraniliprole + thiamethoxam and chlorantraniliprole showed the greatest lethal and sublethal effects, indicating their potential for S. frugiperda management. Field studies are warranted to validate these laboratory findings and optimize application rates within integrated pest management programs.