Insecticidal and antifeedant effects of eugenol on Hyphantria cunea (Lepidoptera: Erebidae) larvae and associated physiological responses

The insecticidal activity of eugenol has been acknowledged, while its biological activity and underlying mechanisms against Lepidopteran pests are still not fully elucidated. This study investigates the lethal and antifeedant effects of eugenol on Hyphantria cunea larvae, while elucidating its insecticidal mechanism through the lens of digestive function, energy metabolism, and antioxidant defense systems. The results demonstrated that eugenol had biological toxicity against H. cunea larvae, manifesting as mortality, feeding deterrence, and decreased food utilization efficiency. Further analysis reveals that eugenol significantly impaired the larval digestive function by inhibiting the activities of α-amylase, lipase, and trypsin, as well as downregulating the expression of six digestive enzyme genes. Furthermore, eugenol treatment suppressed the activity of key rate-limiting enzymes in the glycolytic pathway and tricarboxylic acid cycle (hexokinase and nicotinamide adenine dinucleotide-isocitrate dehydrogenase), downregulated the expression of associated genes, and reduced Na+/K+-ATPase activity, ultimately leading to a decrease in ATP supply and a delay in hydrolysis. Although eugenol can activate antioxidant enzymes and upregulate the expression of related genes, the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) still increase. Additionally, eugenol impaired the feeding performance of larvae on host plants while exhibiting low toxicity to non-target aquatic organisms. In conclusion, our findings demonstrate that eugenol represents a promising and effective alternative for the control of the invasive pest H. cunea.