Chemical Composition and Insecticidal Activities of the Essential Oil of Clinopodium chinense (Benth.) Kuntze Aerial Parts against Liposcelis bostrychophila Badonnel

Water-distilled essential oil from Clinopodium chinense (Labiatae) aerial parts at the flowering stage was analyzed by gas chromatography-mass spectrometry. Thirty-five compounds, accounting for 99.18% of the total oil, were identified, and the main components of the essential oil of C. chinense were spathulenol (18.54%), piperitone (18.9%), caryophyllene (12.04%), and bornyl acetate (8.14%). Based on bioactivity-directed fractionation, bornyl acetate, caryophyllene, and piperitone were identified from the essential oil. The essential oil possessed fumigant toxicity against booklice (Liposcelis bostrychophila) with a 50% lethal concentration (LC50) value of 423.39 μg/liter, while the isolated constituents, bornyl acetate and piperitone, had LC50 values of 351.69 and 311.12 μg/liter against booklice, respectively. The essential oil also exhibited contact toxicity against L. bostrychophila with an LC50 value of 215.25 μg/cm(2). Bornyl acetate, caryophyllene, and piperitone exhibited acute toxicity against booklice with LC50 values of 321.42, 275.00, and 139.74 μg/cm(2), respectively. The results indicated that the essential oil and its isolated constituents have potential for development into natural insecticides or fumigants for control of insects in stored grains.