| To study and develop the precious insecticidal plant Periploca sepium Bunge, the insecticidal constituents were isolated by bioassay-guided fractionation, and he mechanism of main insecticidal constituents were also preliminary studied by observation of semeiology and histology, and physiological and biochemical research in this thesis. The main results were as follows:1. The bioassay results of the extract of petroleum ether, ethyl acetate and methanol from the velamen of Periploca sepium Bunge showed that the stomach toxic effect of methanol extract on armyworms was strongest. The corrected mortality of the armyworms after 48 hours was 86.89% at the concentration of 50mg·mL-1.2. By means of non-pressurized column chromatography and preparative HPLC three compounds, Z01,Z02,Z03 were isolated from the methanol extract of Periploca sepium Bunge in the guidance of bioassay-guided fractionation. On the basis of spectral data, Z01,Z02,Z03 were identified as periplocoside A,periplocoside NW and ergosterol, respectively.3. Periplocoside NW exhibited an obviously higher insecticidal activity than that of Periplocoside A. Periplocoside NW also exhibited a strong stomach toxicity against third instar Plutella xylostella (LC50=866.17mg·L-1), Mythimna separata (LC50=927.92mg·L-1) and Pieris rapae (LC50=1107.08mg·L-1) after 24 hours and it has no action of contact poisoning significantly against the testing insects above. In addition, Periplocoside NW exhibited some lethal activity against Aphis gossypii (LC50 =1743.17mg·L-1), Tetranychus cinnarinus (LC50 =2179.49mg·L-1), third instar Musca domestica larvae (LC50 =714.94mg·L-1) and third instar Culex pipiens pallens larvae (LC50 =653.29mg·L-1) after 24 hours.4. By the determination of physiological and biochemical indexes of semeiology,histology and digestive enzyme, the results indicated that after 4 hours of being treated by Periplocoside NW, the specific activity of amylase decreased in comparison with the contemporaneous control. The amylase was inhibited at a greater degree as time was prolonged. While after 4 hours, the specific activity of protease increased in comparison with the contemporaneous control. The protease was activated at a greater degree as time was prolonged. From light microscopic study, the microvilli layer of goblet cells and columnar cells in the midgut of Mythimna separate larvae were damaged. Thus, the barrier function of the midgut's intestinal wall has been directly destroyed, which made the entry of poison into haemolymph easier and affected other targets. It is estimated that Periplocoside NW is a damaging agent of alimentary canal, which can directly damage the midgut cells of Mythimna separate. And it can help haemolymph come into the midgut through intestinal wall which lead to the midgut expanded. As the blood in the midgut increased, the intestinal wall ruptured and the midgut disintegrated which caused the death of the tested insects finally. A further tem observation showed that besides microvilli in the midgut's intestinal wall of Mythimna separate which has been damaged, organelles in the cells like endoplasmic reticulum, mitochondria, nuclear membrace, etc. have been damaged, too. It showed that the effect of Periplocoside NW on cells and organelle of the midgut might be one reason for the death of the tested insects.
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