Comparative toxicity and biochemical impacts of certain recommended insecticides against Spodoptera littoralis (Lepidoptera: Noctuidae)

Abstract The cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae), is a destructive agricultural pest that causes significant yield losses in various crops. The extensive use of chemical insecticides necessitates a comprehensive evaluation of their toxicological efficacy and sublethal biochemical effects to support sustainable pest management strategies. This study aimed to evaluate the comparative toxicity and biochemical effects of four insecticides (emamectin benzoate, chlorantraniliprole, lufenuron, and indoxacarb) against fourth-instar larvae of laboratory-reared cotton leafworm Spodoptera littoralis (Boisd.). Among all the tested insecticides, emamectin benzoate was the most effective (LC50= 0.399 mg/L), whereas indoxacarb was the least effective (LC50= 13.062 mg/L). Sublethal effects were assessed by examining the biochemical responses of fourth-instar larvae exposed to LC25 concentrations of 0.19, 3.38, 3.052, and 8.008 mg/L for the respective insecticides under controlled laboratory conditions. Enzymatic activity was monitored at 1, 3, and 5 days post-treatment. The results revealed significant alterations in total protein and carbohydrate contents, as well as the activities of key enzymes involved in carbohydrate metabolism (invertase, trehalase, and amylase), transamination (AST and ALT), phosphatase function (ALP), and detoxification enzymes (α-esterase), compared with those in the untreated controls. These findings provide mechanistic insights into insecticide-induced metabolic and enzymatic disruptions and highlight the importance of incorporating biochemical indicators into pesticide evaluation frameworks to support more effective and sustainable insect pest management programs.