Exploring the chemical profiling and insecticidal properties of essential oils from fresh and discarded lemon peels, Citrus limon against pulse beetle

Essential oil (EO) of Citrus limon fresh (LF) and lemon waste peel (LW) was extracted using the hydro distillation method. A total of 17 chemical constituents (97.02–97.26%) were identified using GC, GC-MS, and NMR techniques. Major monoterpene hydrocarbons including d-limonene (52.42–54.17%), α-terpineol (16.82–21.15%), β-pinene (6.74–9.15%) and γ-terpinene (2.16–3.59%) were further identified using ¹H and ¹³C NMR analysis. Furthermore, extracted EOs, their synergistic combinations and major constituent (d-limonene) were evaluated for fumigant toxicity, repellence, and ovipositional inhibitory (OI) potential using without food and with food conditions against pulse beetle, Callosobruchus chinensis and Callosobruchus maculatus. d-limonene was found to be most effective against C. chinensis and C. maculatus followed by LW oil in all the evaluated assays. EO of LW was found more effective against C. chinensis (LC₅₀ = 2899.11 μl L⁻¹) without food after 96 h than lemon fresh. Among synergistic combinations, LW and LF at 3:1 ratio without food reported more effective to C. chinensis (LC₅₀ = 277.85 μl L⁻¹) and C. maculatus (LC₅₀ = 322.38 μl L⁻¹) without food after 96 h. In repellent assay, EO of LW also displayed higher repellent to both species (RC₅₀ = 430.71 to 525.56 and μl L⁻¹). EO of LW showed higher OI (50.14 ± 3.09%) against C. chinensis at higher concentration after 24 h. EOs of LF and LW also inhibited glutathione -S-transferase and acetylcholine esterase activity in C. chinensis and C. maculatus.