Antifeedant Activities And Action Mechanism On Secondary Substances From Xanthium Sibiricum Against Insects

Xanthium sibiricum Patr was extracted and purified for its active compounds with antifeedant effect against Mythimna separate Walker and Pieris rapae Linnaeus. And then, the effect of the active fractions on digestive enzymes and structure of midgut issues of P. rapae larve were studied. Finally, the chemical ingredian of the active fractions were analysed. The results are as follows:(1) The effects of antifeedant of extracts from X.sibiricum on Mythimna separate Walker and Pieris rapae Linnaeus was investigated with leaf-discs methods. The results showed that the chloroform extraction X.sibiricum had obviously antifeedant effect to the 4th larvae of M. separate and P. rapae, the AFC50 were 24.40 mg/mL and 7.20mg/mL. By silica gel column chromatograghy methods, nine fractions were achived from the chloroform extracts of X. sibiricum. And the antifeedant activity of fraction 8th and fraction 9th were the strongest activities, with their AFC50 value against P. rapae being 22.89ug/mL and 14.68ug/mL, respectively.(2) The effect of the 8th fraction and 9th fraction from the chloroform extraction of X.sibiricum on the activity of midgut digestive enzymes of P. rapae were studied. The results showed that the amylase and protease activity were distinctly inhibited. After treatment 36h, the protease inhibition ratio was 54.08% and 56.83%, respectively, and the inhibition ratio of amylase was 55.45% and 60.02%, respectively. Minewhile, midgut carboxyl esterase activity was inhibited with esterase inhibition ratio being 96.90% and 98.30% after treatment 36h. But the esterase activities of hemolymph were induced after treatment. With the time going, the activities come to normal.(3) The effect of the 8th fraction and 9th fraction from the chloroform extraction of X.sibiricum Patr. on the structure of midgut tissues of P. rapae were studied. The results showed that the structure of midgut tissues of P.rapae larve exhibited distinct pathological change after treatment. The micro-rods of cylindrical epithelium dissolved, and the goblet cells in epithelium of midgut showed deformed.(4) The chemical compounds of the 8th fraction and 9th fraction from X. sibiricum were analyzed by using gas chromatography-mass spectrometr. The results showed that they both are containing stigmasterol,β-sitosterol, and small quantities of campesterol. Particulary, the 8th fraction containingβ-sitosterol more compared with the 9th fraction containing stigmasterol more.In short, three sterols with the higher antifeedant effect on M. separate and P. rapae were found in fraction 8th and 9th from X. sibiricum, which significantly inhibited the activity of the protease, amylase and carboxyl esterase in midgut of P. rapae 4th larve. But esterase activities against P. rapae hemolymph were induced. The structure of midgut epithelium issues of P. rapae larvae showed damaged by the sterols.