Insecticidal Metabolites from the Rhizomes of Veratrum album against Adults of Colorado Potato Beetle, Leptinotarsa decemlineata

The dried rhizomes of Veratrum album were individually extracted with CHCl3, acetone, and NH4OH/benzene to test the toxic effects against the Colorado potato beetle, Leptinotarsa decemlineata, which is an important agricultural pest. Fifteen compounds in various amounts were isolated from the extracts using column and thin-layer chromatography. The chemical structures of 14 compounds were characterized as octacosan-1-ol (1), -sitosterol (2), stearic acid (3), diosgenin (4), resveratrol (5), wittifuran X (6), oxyresveratrol (7), -sitosterol 3-O--D-glucopyranoside (8), diosgenin 3-O--L-rhamnopyranosyl-(12)--D-glucopyronoside (9), oxyresveratrol 3-O--D-glucopyranoside (10), jervine (11), pseudojervine (13), 5,6-dihydro-1-hydroxyjervine (14), and saccharose (15) using UV, IR, MS, H-1- and C-13-NMR, and 2D-NMR spectroscopic methods. However, the chemical structure of 12, an oligosaccharide, has not fully been elucidated. Compounds 4, 6, 9, and 10 were isolated from V. album rhizomes for the first time in the current study. The toxic effects of three extracts (acetone, CHCl3, and NH4OH/benzene) and six metabolites, 2, 2+4, 5, 7, 8, and 11, were evaluated against the Colorado potato beetle. The assay revealed that all three extracts, and compounds 7, 8, and 11 exhibited potent toxic effects against this pest. This is the first report on the evaluation of the toxic effects of the extracts and secondary metabolites of V. album rhizomes against L. decemlineata. Based on these results, it can be concluded that the extracts can be used as natural insecticides.