Abstract: The toxicity of lambda-cyhalothrin against adult Monochamus alternatus (a vector insect of pine wilt disease) was determined using the film method, and the responsive changes of key metabolic enzymes under sublethal stress were analyzed. Enzyme kinetic studies were conducted using the surviving adults treated with the 72-hour median lethal concentration (LC₅₀) as the subjects. The findings revealed that significant time-dependent toxicity, with complete cessation of feeding activity observed at concentrations ≥ 50 mg/L. The cytochrome P450 enzymes (P450) play a dominant role in the detoxification pathway; glutathione S-transferase (GST) and carboxylesterase (CarE) activities showed initial induction followed by inhibition, and sustained inhibition, respectively; while key antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) reached peak activity at 48 hours of stress. In conclusion, this study confirms that lambda-cyhalothrin inhibits the survival of M. alternatus through its time-cumulative toxicity and induced metabolic imbalance.