Seasonal metabolic profiling of Valencia orange leaf essential oil using GC coupled with chemometrics, nano-formulation, and insecticidal evaluation: in vivo and in silico

Abstract

Mosquitoes and mosquito-borne infectious diseases are a global challenge, especially with increased resistance to synthetic insecticides. The foregoing study aimed to utilize the essential oil of leaves of Citrus sinensis var. Valencia as a cheap, safe, eco-friendly (green), and effective alternative to chemical insecticides. Essential oil samples were collected from fresh and dried leaves across different seasons. They are subjected to hydrodistillation and then GC analysis to be compared. Seventy-seven compounds were detected in all samples where monoterpene hydrocarbons represented the most abundant class of hydrocarbons in fresh leaves (52.6–74.4%) and dried leaves (58.6–66.9%). Sabinene (8.26–29.2%), delta-3-carene (8.23–16.4%), D-limonene (2.50–11.2%), and β-myrcene (2.40–4.93%) were the major monoterpene hydrocarbons in all seasons. Oxygenated monoterpenes comprising β-linalool, citronellal, terpinen-4-ol, β-citral, and α-citral exhibited also appreciable percentages in fresh (21.2–43.4%) and dried leaves (23.4–33.0%). Hierarchical cluster analysis (HCA) and principal component analysis (PCA) effectively segregated all samples into three discriminate clusters where, β-linalool, terpinen-4-ol, β-elemene enantiomer, sabinene, and β-phellandrene constitute the main discriminatory biomarkers. Essential oil of fresh spring leaves (FS) was chosen for nano-formulation adopting the hot emulsification method. Both FS sample and the prepared nano-hexosomal formula were screened against the 3rd instar larvae Culex pipiens L. (common house mosquito). LC₅₀ and LC₉₅ values of FS and oil loaded nano-formula were (48 and 30 552 mg L⁻¹) and (30 and 1830 mg L⁻¹) respectively. α-Citral followed by citronellal showed the best fitting within the binding sites of acetylcholine esterase enzyme utilizing molecular docking. Thus, it can be concluded that Valencia orange leaf as a nano-formulation could serve as an effective and sustainable insecticidal agent.