| One hundred seventeen species of plants collected from Guangxi zhuang autonomous region were extracted with methanol. Insecticidal activities of these extracts against Lipaphis erysimi Kaltenbach were determined by topical application. According to the insecticidal activity, Blumea megacephala Chang et Tseng, which had high contact activity against Lipaphis erysimi Kaltenbach, was selected to be further investigated for active ingredients. And the extract was separated by liquid -liquid extraction and purified through column chromatograghy. Primary mechanism was investigated through the change of several enzymes.The contact activities of 122 methanol extracts of 117 plants against Lipaphis erysimi Kaltenbach were determined by topical application in laboratory. Results showed that 2 plant extracts had high contact activity, with a corrected mortality of >80% at 10μg/larvae after 24 hours, they were that of Blumea megacephala Chang et Tseng, Pilea cavaleriei Levl. 15 plant extracts had medium activity, their corrected mortality ranging from 50% to 80%, they were that of Osbeckia crinita Benth. In Wall., Gnetum montanum Markgr, Evodia lepta Merr., Abrus precatoriusL., Toxicodendron Succedaneum(Linn.), Mirabilis jalapa Lim., Croton cavaleriei Gagnep, Cibotium barometz(Linn.)J.Sm., Litsea cuheha(Lour.)Pers., Diplocyclos palmatus(L.)C., Stephania cepharantha Hayata, Curcrligo orchioides Gaerth., Coix lacroyma jobiL., Daphniphyllum calycinum Benth, Piper puberulum(Benth.)Maxim. The other plants studied had low activity, the corrected mortality being below 50%.In oder to further compare the contact activities of plant extracts, Contact toxicities of 8 plant extracts to Lipaphis erysimi Kaltenbach were determined. The extract from branches and leaves of Blumea megacephala had the highest activity against Lipaphis erysimi Kaltenbach, with a LC50 value of 3.9597μg/female. Relative toxicities of the eight plant extracts, ranging from highest to lowest, were: Blumea megacephala Chang et Tseng>Pilea cavaleriei Levl.>Toxicodendron Succedaneum(Linn.) >Abrus precatoriusL. >Piper puberulum(Benth.)Maxim. >Croton cavaleriei Gagnep. >Coix lacroyma jobiL. >Osbeckia crinita Benth. In Wall.According to above results, Blumea megacephala Chang et Tseng was selected for further investigation. Contact activities were determined for the methanol extracts from different parts of Blumea megacephala Chang et Tseng to Lipaphis erysimi Kaltenbach. Extracts of stem and leaf had high contact activity , the corrected moriality were 60.47% and 64.15% after 24 hours; extracts of root and flower studied had low activity, the corrected mortality were21.19% and 41.37%.The resulst showed the extract of stem and leaf against Lipaphis erysimi Kaltenbach had high contact activity, suggesting that the active ingredients be mainly existed in the extract of stem and leaf.The methanol extract from stem and leaf of Blumea megacephala Chang et Tseng was preliminarily separated into four parts by liquid -liquid extraction with petroleum ether, ethylacetate, n-butanol and water. The contact activities of four parts by liquid -liquid extraction against Lipaphis erysimi Kaltenbach were determined by topical application in laboratory. Results showed that at 5μg/larvae, the activity of petroleum ether extract against Lipaphis erysimi Kaltenbach was much higher than that of the others,its corrected mortality rate being 68.96% after 24h; the corrected mortality rate of ethylacetate fraction was 20.25% after 24h ; the n-butanol part and water part had a certain insecticidal activity, but these activities were lower than that of petroleum ether part and ethylacetate part, suggesting that the active ingredients be mainly existed in the petroleum ether extract.By silica gel column chromatograghy and tested by TLC analysis, the petroleum ether part was separated into 17 groups. The activity of group 8 had the strongest activity, the corrected mortality rate being 89.92% at 3μg/female after 24h; the activity of group 17 had the stronger activity, the corrected mortality rate being 82.95%. The corrected mortality of group 1, 2, 4, 6 and 9 on Lipaphis erysimi Kaltenbach were above 70%,the contact activities of group 1, 2, 4, 6 and 9 were 72.51%, 70.86%, 70.01%, 73.17% and 74.95%. The corrected mortality of 3,14,15 group on Lipaphis erysimi Kaltenbach were above 60%, the contact activities of group 3, 14 and 15 were 62.32%, 67.05% and 61.9%.By activity-directed isolation method, the active ingredients were almost exist in every different groups after further separation and purification of active ingredients by silica gel column chromatography, guessing the result may be several kinds active ingredient coordination effects.Trial of the methanol extract of Blumea megacephala Chang et Tseng against Lipaphis erysimi Kaltenbach in pot was conducted, and the results showed that the control efficacy of two preparations was high on Lipaphis erysimi Kaltenbach. After 24h, 48h, 72h, the control efficacy of 10 times of 20%EC of Blumea megacephala Chang et Tseng on Lipaphis erysimi Kaltenbach were 57.78%, 77.19% and 84.79%. After 24h, 48h, 72h, the control efficacy of 5 times of 10% EW of Blumea megacephala Chang et Tseng on Lipaphis erysimi Kaltenbach were 74.44%, 84.79% and 89.14%. With the concentration dropped, the control efficacy would be fell down. After 24h,48h,72h, the control efficacy of 30 times of 20%EC of Blumea megacephala Chang et Tseng on Lipaphis erysimi Kaltenbach were 37.78%, 54.38% and 60.90%. After treating of 24h,48h,72h,the control efficacy of 20 times of 10%EW of Blumea megacephala Chang et Tseng on Lipaphis erysimi Kaltenbach were 44.44%, 60.90% and 71.76%.Influence of Blumea megacephala Chang et Tseng on protein content and three kinds of protective enzymes of Lipaphis erysimi Kaltenbach was studied, after the treatment of the methanol extract of Blumea megacephala Chang et Tseng, the activity of CAT declined, the activity of SOD rised, while the content of protein and the activity POD could not be inhibited.
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