Insecticidal activities of essential oils, Gaultheria fragrantissima and Illicium verum, their components and analogs against Callosobruchus chinensis adults

Abstract

Insecticidal activity of croton, linaloe berry, rosewood, star anise, wintergreen oils, methyl salicylate and 8 analogs against Callosobruchus chinensis adults was assessed. The 24-h LC50 values against adult C. chinensis were 3.14, 6.68, 8.59, 8.90 and 10.23mg/L air for wintergreen, star anise, croton, linaloe berry and rosewood oils. Analyses by gas chromatography (GC) and GC-mass spectrometry led to the identification of 2 and 18 compounds from G. fragrantissima wintergreen and star anise I. verum oils, respectively. Among the compounds identified, methyl salicylate consisted of 99.9% of wintergreen oil and trans-anethole did 91.0% of I star anise oil. To elucidate structure–activity relationship of methyl salicylate and trans-anethole, fumigant and contact toxicities of methyl salicylate, methyl 3-hydroxybenzoate, methyl 4-hydroxybenzoate, methyl 2-methoxysalicylate, methyl 2-acetoxysalicylate, methyl benzoate, salicylic acid, trans-anethole and 1-methoxy-4-propylbenzene were investigated. Methyl 3-hydoxybenzoate, methyl 4-hydroxybenzoate, methyl 2-methoxybenzoate, and methyl 2-acetoxybenozate did not show fumigant activity. The 24-h LC50 values were 3.48, 5.36, 6.39 and 9.27mg/L air for methyl salicylate, methyl benzoate, trans-anethole, and 1-methoxy-4-propylbenzene, respectively. However, all the compounds tested except methyl 3-hydroxybenzoate and methyl 4-hydroxybenzoate showed contact toxicity. The 24-h LD50 values (μg/beetle) were 28.89, 33.27, 33.56, 44.81 56.31, 38.59 and 69.20 for methyl salicylate, methyl 2-acetobenzoate, methyl 2-methoxybenoate, methyl benzoate, salicylic acid, trans-anethole and 1-methoxy-4-propylbenzene, respectively. Structural differences were identified that may contribute to understanding the insecticidal activities of methyl salicylate and trans-anethole.