Insecticidal and biochemical impacts with molecular docking analysis of three essential oils against Spodoptera littoralis (Lepidoptera: Noctuidae)

As an eco-friendly alternative to chemical insecticides, essential oils (EOs), have gained recognition for their pest-control properties. In this study, the toxicity, biochemical activity and molecular docking analysis of marjoram (Origanum majorana), citronella (Cymbopogon winterianus), and rosemary (Rosmarinus officinalis) EOs were investigated against 2nd instar larvae of cotton leafworm (Spodoptera littoralis) Boisaduval. GC–MS analysis of the chemical composition of the tested EOs showed that O. majorana, C. winterianus, and R. officinalis EOs contained 12, 20, and 5 components, respectively. O. majorana was composed largely of monoterpenoid molecules (47.12%), while both C. winterianus and R. officinalis were composed mainly of monoterpenes (84.39 and 92.16%, respectively). The toxicity tests revealed that R. officinalis EO had the highest insecticidal activity (LC50 = 2526.08 mg/L) against S. littoralis larvae. In addition, the tested EOs resulted in development disruption in S. littoralis, with R. officinalis EO showing the highest potency. Cymbopogon winterianus significantly inhibited the activity of detoxifying enzymes, namely, Carboxylesterase (α- and β-esterase), Glutathione S-Transferase (GST) and Cytochrome P450 (P450s). Similarly, C. winterianus and O. majorana inhibited the activity of superoxide dismutase (SOD). However, no significant difference in CAT activity was observed between the treated larvae and the control. As a result of docking analysis, the interaction of the main constituent of the tested EOs with GST occurred in the following order terpinen-4-ol> (Z)-citral> α-pinene correspondence to their energy score of −4.7386, −4.6491, and −4.5097 kcal/mol, respectively. The obtained results demonstrate the potential use of O. majorana, C. winterianus and R. officinalis EOs in S. littoralis management programs.