关键词: 豆薯种子, 杀虫成分, 化合物结构, 毒力, 12α-羟基鱼藤酮

Abstract: Insecticidal compounds from seeds of yam bean Pachyrrhizus erosus (L.) Urban were studied in order to determine their insecticidal toxicity. Using the 4th instar larvae of Aedes albopictus as target insect pest, the active ingredients were isolated from the methanol extracts of the seeds by activity-directed fractionation with column chromatography and thin layer chromatography (TLC), and identified predominantly on the basis of NMR data. Insecticidal activities and action mode of these compounds were determined against the 4th instar larvae of A. albopictus, Aphis gossypii apterae, the 3rd instar larvae of both Herse convolvuli and Plutella xylostella by leaf dip method, topical application and leaf disk method, respectively. Fourteen compounds were isolated and identified, which were 12α-hydoxyrotenone, pachyrrhizine, 12α-hydoxypachyrrhizone, 12α-dehydropachyrrizone, α-naphthoflavone, 7-methoxyflavanone, 12a-hydroxydolineone, 6-methoxyflavone, 4′-hydoxyflavanone, quercetin dehydrate, 5-methoxyflavone, 7-hydroxyflavone, 3′-hydoxyflavanone and 3-hydroxyflavone. The results of bioassay showed that among the 14 compounds, the former seven possessed insecticidal activity against A. albopictus larvae, with corresponding LC₅₀ values at 24 h after treatment being 25.0, 51.1, 196.2, 48.4, 98.9, 107.2 and 15.6 mg/L, respectively; the former six exhibited insecticidal activity against A. gossypii apterae, with the LC₅₀ values at 24 h after treatment being 1.5, 10.9, 80.7, 66.8, 32.1 and 112.8 mg/L, respectively; the former five and 12α-hydroxydolineone had insecticidal activities against H. convolvuli larvae; 12α-hydoxyrotenone exhibited stomach toxicity to the 3rd instar larvae of P. xylostella, with the LD₅₀ values being 17.3 μg/individual at 24 h after treatment, while 7-methoxyflavone only possessed weak growth inhibition activity to the insect pest. Nine-compounds (6-methoxyflavone, 4′-hydoxyflavanone, quercetin dehydrate, α-naphthoflavone, 7-methoxyflavanone, 5-methoxyflavone, 7-hydroxyflavone, 3′-hydoxyflavanone and 3-hydroxyflavone) were isolated from the seeds of P. erosus for the first time. There were seven insecticidal compounds altogether from the seeds, whose action modes to the different tested insects were different. The main insecticidal ingredient was not rotenone but 12a-hydoxyrotenone.

Key words: Pachyrrhizus erosus seeds, insecticidal ingredients, chemical structure, toxicity, 12α-hydoxyrotenone