Efficacy and biochemical analysis of sub-Lethal concentrations of some insecticides against Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

The study assessed the toxicity and biochemical effects of emamectin benzoate, lufenuron, chlorpyrifos, and spinosad on Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) 2nd and 4th instar larvae. Results revealed that, 2nd instar larvae were more sensitive than 4th instar larvae to the four insecticides. Emamectin benzoate exhibited the highest toxicity (LC50: 0.166 ppm and 0.23 ppm), followed by lufenuron, chlorpyrifos, and spinosad. Biochemical analysis revealed significant metabolic disruptions. Total soluble protein levels increased after emamectin and spinosad treatments but decreased with lufenuron. Carbohydrate levels rise with emamectin and lufenuron but dropped with chlorpyrifos and spinosad, while lipid content decreased across all treatments, indicating high energy demands. Glutathione S-transferase (GST) activity increased substantially, reflecting enhanced detoxification processes, particularly with emamectin. Alpha and beta esterase activities also increased, further supporting detoxification mechanisms. Alkaline phosphatase activity showed pronounced increases, especially with emamectin, while acid phosphatase levels declined, suggesting disrupted lysosomal activity. Acetylcholinesterase (AChE) activity decreased in all treatments, with chlorpyrifos causing the greatest inhibition. Significant increases in GOT/AST and GPT/ALT activities indicated cellular damage and metabolic stress, with chlorpyrifos showing the strongest effect, followed by emamectin. These findings highlight the varying toxicity levels and metabolic disruptions caused by the tested insecticides, providing valuable insights for supporting management strategy of S. frugiperda.