Analysis of the Essential Oil of Dipsacus japonicus Flowering Aerial Parts and its Insecticidal Activity against Sitophilus zeamais and Tribolium castaneum

Water-distilled essential oil from the aerial parts of Dipsacus japonicus Miq. (Dipsacaceae) at the flowering stage was analysed by gas chromatography-mass spectrometry (GC-MS). Forty-six compounds, accounting for 96.76% of the total oil, were identified and the main compounds of the essential oil were linalool (11.78%), trans-geraniol (8.58%), 1,8-cineole (7.91%), beta-caryophyllene (5.58%), alpha-terpineol (5.32%), beta-selinene (5.15%), and spathulenol (5.04%). The essential oil of D. japonicus possessed contact toxicity against two grain storage insects, Sitophilus zeamais and Tribolium castaneum adults, with LD50 values of 18.32 mu g/adult and 13.45 mu g/adult, respectively. The essential oil of D. japonicus also exhibited pronounced fumigant toxicity against S. zeamais (LC50 = 10.11 mg/l air) and T castaneum adults (LC50 = 5.26 mg/l air). Of the three major compounds, 1,8-cineole exhibited stronger fumigant toxicity than the crude essential oil against S. zeamais and T castaneum adults with LC50 values of 2.96 mg/l air and 4.86 mg/l air, respectively.