Résumé:
Synthetic chemicals can have harmful effects on both humans and plants, leading to health issues like toxicity and pollution that disrupt ecosystems and damage plant growth; meanwhile essential oils offer safer, and natural alternatives. In this context, the objective of this research was to study the chemical composition, as well as the antioxidant, anti-enzymatic, and insecticidal activities, of essential oils from two medicinal plants, Laurus nobilis and Aloysia citrodora, along with their major compounds: 1,8-cineole, methyleugenol, citral, and limonene. The analysis of the chemical composition of the essential oils was carried out by gas chromatography-mass spectrometry (GC-MS). Six different in vitro tests, DPPH scavenging, ABTS cation radical, reducing power, β-carotene/linoleic acid bleaching, cupric reducing antioxidant capacity, and phenanthroline assay were performed to evaluate the antioxidant properties of Laurus nobilis, Aloysia citrodora essential oils, and their major compounds; furthermore, the antienzymatic activity was carried out against six enzymes: acetylcholinesterase, butyrylcholinesterase, tyrosinase, urease, α-glucosidase, and α-amylase. The insecticidal potential of essential oils, and their major compounds was assessed against three Aphid’s species: Aphis fabae, Rhopalosiphum maidis, and Myzus persicae. We employed three different methods: contact toxicity, fumigant toxicity, and field efficacy testing. The results of the chemical composition analysis showed that Laurus nobilis essential oil is primarily composed of 1,8-cineole (26.43%), methyleugenol (13.55%), α-Terpinyl Acetate (11.77%), and linalool (10.19 %). In contrast, the main constituents of Aloysia citrodora essential oil were found to be citral (13.80%), limonene (12.16%), Neral (10.67%), Bicyclogermacrene (10.03%),
Isospathulenol (6.06%), caryophyllene oxide (6.82%) and p-cymene (4.5%). the results of antioxidant activity, demonstrated that L. nobilis essential oil, along with 1,8-cineole and methyleugenol, exhibited strong antioxidant properties across all test methods. In contrast, A. citrodora essential oil and its major compounds, citral and limonene, showed no antioxidant activity. The assessment of enzymatic inhibition revealed that the examined volatile plant extracts, and their primary constituents exhibited selective efficacy, demonstrating potent inhibitory effects on certain enzymes while remaining inert against others. The insecticidal activity data indicates that both essential oils, along with the major compounds, showed strong contact and fumigant toxicities, against A. fabae, R. maidis, and M. persicae. Field experiments showed that Laurus nobilis essential oil had significant control effects, at a concentration
of 0.4 L/m² achieving 86.81%, 80.67%, and 78.23% mortality for A. fabae, R. maidis, and M. persicae, respectively. Similarly, Aloysia citrodora essential oil shows mortality of 90.33% in adults of M. persicae, followed by 86.67% in A. fabae, and 84.00 % in R. maidis. However, the toxicity varied based on insect species, concentration, and exposure duration. Both oils proved more potent than their individual compounds in all the biological activities tested. The results showed that these essential oils and their major compounds could serve as alternatives to chemical synthetic preservatives and pesticides.
