Potential of Thymol as a Natural Solution against the Maize Weevil [Sitophilus zeamais (Motsch.)]: in Vitro, In Vivo and In Silico Studies

Using essential oils (EOs) and their primary compounds to protect stored grains from insect infestations offers a promising alternative to synthetic insecticides. This study tested thymol, a major constituent of thymus EO (Thymus vulgaris), for its insecticidal effects on the maize weevil, Sitophilus zeamais (S. zeamais). The repellent activity was evaluated using a preferred zone method, where insects were given the choice between treated and untreated areas. This method demonstrated significant repellent effects across all tested concentrations, with repellency rates exceeding 80% at a concentration of 300 µL/mL. In fumigant activity tests, the concentration of 300 μL/mL achieved highly significant results, with a mortality rate of 98% by the fourth day of treatment. Additionally, topical exposure of insects to thymol showed significant insecticidal activity, with mortality rates of 81% and 100% at doses 0.06 and 0.12 μL per insect, respectively. Insects exposed to grains treated with concentrations of 1.2, 1.8, and 2.4 µL/mL exhibited 100% mortality within 7 days. Significant differences were also found between treated and untreated grains for weight loss, hole percentage, and the inhibition of progeny insects, irrespective of the concentration. The molecular docking simulations of thymol against the Acetylcholinesterase protein (PDB ID: 7E3H), showed that thymol interacts strongly with this protein target (binding energy of -7.291 kcal/mol), suggesting potential neurotoxic effects on S. zeamais. These findings highlight thymol's potential as a natural and effective alternative to synthetic insecticides for the protection of stored grains against weevil infestations, offering a promising solution for safer post-harvest management.