Temperature plays a pivotal role in shaping the physiological responses of mustard aphid (Lipaphis erysimi Kaltenbach) morphs, influencing their enzymatic activity and oxidative stress management. This study examined their enzymatic activities using spectrophotometric assays, with SOD and CAT evaluated as markers of antioxidant responses and LPO as an indicator of oxidative damage in alate (winged) and apterous (wingless) morphs under field conditions during the Rabi season at the Agricultural Research Farm, Banaras Hindu University. Aphid populations peaked at 13.6°C in mid-January, correlating with significantly higher enzymatic activity in alate morphs, which exhibited elevated SOD (0.405 ± 0.042 U/mg protein) and CAT (0.046 ± 0.011 U/mg protein) levels, reflecting their enhanced oxidative stress defences during dispersal. Apterous morphs, adapted for reproduction, demonstrated lower SOD (0.314 ± 0.067 U/mg protein) and CAT (0.023 ± 0.006 U/mg protein) activities, consistent with their sedentary lifestyle and reduced exposure to temperature-induced stress. Lipid peroxidation was notably higher in alates (0.210 ± 0.035 nmol-TBARS/mg protein) compared to apterous morphs (0.068 ± 0.004 nmol-TBARS/mg protein), underscoring the oxidative cost of flight. The overall study results corroborate the hypothesis that temperature variability strongly influences the enzymatic responses of L. erysimi morphs, providing insights into their physiological plasticity and potential vulnerabilities. Understanding these mechanisms can inform pest management approaches by targeting the biochemical pathways involved in stress adaptation.