Effect of Constant and Fluctuating Temperatures on the Activity of Enzymes and the Biochemical Composition of the Fall Armyworm (FAW) Spodoptera frugiperda (Smith)

Abstract

This study employed a controlled laboratory experimental design to investigate the effect of temperatures (20, 25, and 30°C) on the enzymatic activity and biochemical composition of Fall armyworm (FAW) Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) instar larvae using laboratory strain and field strain. The biochemical composition and enzymatic activities of S. frugiperda larvae were significantly influenced by temperature. Carbohydrate and protein content were highest at 25°C (25.80 mg/g and 60.13 mg/g body weight, respectively), while lipid content remained stable except for a significant reduction at 30°C (4.53 mg/g). Enzymatic activities varied with temperature: Glutamic pyruvic transaminase (GPT) and Glutamic oxaloacetic transaminase (GOT) were elevated at 30°C, while alkaline and acid phosphatases showed temperature-dependent trends. Alpha and beta esterase activities were highest at 30°C, indicating an increased metabolic response, while protease activity peaked at 20°C. Amylase activity was highest in the field strain, declining at lower temperatures, whereas lipase activity peaked at 30°C, suggesting enhanced lipid metabolism under heat stress. These findings indicate that 25°C is optimal for larval biochemical stability, while 30°C imposes metabolic stress, leading to increased energy expenditure. The significantly lower protein content in the field strain suggests that environmental factors impact larval metabolism. Temperature significantly affects biochemical parameters in S. frugiperda larvae, leading to protein and lipid depletion due to increased metabolism. GPT, GOT, and phosphatases showed positive correlations, indicating enhanced amino acid and phosphate metabolism. β-esterase increased, suggesting higher detoxification activity, while protease decreased. Amylase and lipase were strongly correlated with temperature, reflecting increased carbohydrate and lipid digestion. These findings highlight the larvae’s metabolic adaptations to temperature changes, with implications for pest management.