2.6.1. Oxidative Stress Enzyme Assays

After 24 and 96 h post treatment of 2nd-instar larvae of A. ipsilon by LC₁₅ and LC₅₀ values of the lemongrass extract oil, 100 mg of fresh body weight of the surviving larvae of A. ipsilon were transferred to clean and sterilized Eppendorf tubes (1.5 mL). The samples were stored immediately at −20 °C until later analysis. Each treatment and control sample was replicated five times. The treated larvae were homogenized in potassium phosphate buffer (50 mM, pH 7.0) in a 30 µL buffer per 1 mg body weight. The homogenate was centrifuged for 15 min at 7000× g at 4 °C, and the supernatants were used for further analysis.

The catalase (CAT) enzyme activity was estimated [45,46] by measuring the rate of H₂O₂ consumption via absorbance at 510 nm. Lipid Peroxidase Assay Kit (Bio-diagnostic Company, Giza, Egypt) was used for monitoring the formation of malondialdehyde (MDA) at 534 nm [47]. The concentration of total protein of all samples was measured spectrophotometrically based on the Biuret Method using a Protein Biuret Kit (Bio-diagnostic Company, Giza, Egypt).