Chemical Profiling of Two Eucalyptus Essential Oils: Insecticidal and in Silico Inhibitory Activities on Acetylcholinesterase and Chitin Synthase

The insecticidal and inhibitory activities on acetylcholinesterase (AChE) and chitin synthase are crucial for combating Sitophilus oryzae L. (rice weevil), a significant pest responsible for extensive damage to stored grains. These two mechanisms target essential physiological processes in insects, offering an efficient strategy for pest control. This study aimed to validate the pesticidal potential of Eucalyptus globulus and Eucalyptus cinerea through phytochemical analysis of their essential oils (EOs) and evaluation of their insecticidal efficacy against S. oryzae, a common pest in stored cereals. This study has also evaluated the major EO compounds’ inhibitory activity on AChE and chitin synthase. Gas chromatography-mass spectrometry, were used to analyze the essential oils indicating 1,8-cineole as the major compound in E. globulus (67.87%) and in E. cinerea (79.67%). Our EOs demonstarted significant fumigant activity against the rice weevils, E. globulus EO’s showed the high toxicity with (LD50 = 0.053 µL EO/L of air) than E. cinerea EO’s (LD50 = 0.17 µL EO/L of air). The results of the in-silico study demonstrated that Terpinen-4-ol and Dihydrocarveol presented the most potent AChE inhibitory, forming hydrogen bonds with active site residues. In other side, p-Cymene and Terpinen-4-ol exhibited the strongest chitin synthase inhibitory. These findings highlight that E. globulus and E. cinerea essential oils could serve as effective, natural insecticides—targeting key pest defenses like AChE and chitin synthase, offering sustainable and eco-friendly solutions to protect stored cereals.