Characterization of secondary metabolites from the leaves of curry leaf (Murraya koenigii L.) essential oils with insecticidal activities against stored product insects

Abstract

Curry leaf, a significant aromatic shrub belonging to the Rutaceae family, is indigenous to the Indian subcontinent and is widely renowned for its application as a flavor enhancer. Due to specific flavor and fragrance, the leaves of M. koenigii have been recognized for their potential contributions to human health. Curry leaf essential oils have recently received much attention due to their numerous benefits and minimal risk to non-target organisms. This work focused on the comprehensive characterization of secondary metabolites present in the essential oil extracted from curry leaves and aims to evaluate its insecticidal potential in terms of contact, fumigant, and repellent activities against red flour beetle (Tribolium castaneum) and pulse beetle (Callasobruchus maculatus) for first time. Chemical characterization through GC-MS/MS showed that the main chemical compounds within curry leaf essential oil were caryophyllene (28.47%), α-guaiene (13.35%), and α-phellandrene (12.26%). Notably, results from various insecticidal bioassays showed substantial effects upon contact (LC50 at 24 h, 10.56 mg/cm2 for T. castaneum, 20.80 mg/cm2 for C. maculatus) and fumigant toxicities (LC50 at 24 h, 23.93 mg/L air for T. castaneum, 12.96 mg/L air for C. chinensis), alongside repellent activities (at 5 mg/cm2, a mean PR of 90% to T. castaneum and at 5 mg/cm2, C. maculatus demonstrated 80% PR, targeting both insects. Furthermore, a phytotoxicity assessment was performed on stored paddy grains, and neither seedling development nor germination rates were negatively affected. The essential oils extracted from curry leaves exhibit considerable potential as botanical insecticides that are effective against stored-product insects and environmentally benign.