Insecticidal and neurotoxic activity of Origanum vulgare L. essential oil against Dendroctonus mexicanus (Coleoptera: Curculionidae)

The bark beetle Dendroctonus mexicanus Hopkins is one of the most aggressive pests of coniferous forests in Mexico. Herein, we reported the insecticidal and neurotoxic effects of Origanum vulgare L. essential oil (EO) against larvae and adults of this species. The EO was obtained by steam distillation, and its composition was determined by GC-MS. The yield was 0.82% (w/w), and the main constituents were sabinene hydrate (23.67%), carvacrol (7.37%), β-pinene (5.09%), and α-terpinolene (5.04%). Contact toxicity bioassays showed that adults were more susceptible (LD50 = 136.8 μg/insect; LD90 = 354.8 μg/insect) than larvae (LD50 = 247.0 μg/insect; LD90 = 668.0 μg/insect). Acetylcholinesterase (AChE) inhibitory activity showed that carvacrol and thymol were the most active constituents, with IC50 values comparable to the synthetic inhibitor tacrine. Molecular docking analysis revealed that carvacrol and thymol displayed the highest binding affinities on the AChE pocket. These findings highlight the potential of O. vulgare EO and its monoterpene compounds as a sustainable alternative for the control of D. mexicanus.