| The common green bottle fly, Lucilia sericata, which can spread many diseases including dysentery, typhoid, cholera and tuberculosis owing to a lot of pathogen on their body surface. The usage of the chemical insecticide with long-time and high frequency often results in food, environmental pollution and human poisoning et al. Moreover, the L. sericata is resistant to chemical insecticide increasingly. So, one of the effective ways to reduce the L. sericata’s resistance is to find insecticidal substance and exploit new insecticides from natural products. In this investigation, I find that L. sericata appeared the toxicity symptom that was similar with natural pyrethrum when sucked on the flower of Polygonum cuspidatum. Symptoms were mainly manifested as attracting, sucking, exciting, anesthesiaing, convulsing, dying and the body mummified etc. In addition, further research revealed that the extract of ether from ethanol extraction has evidenced toxicity on L. sericata, and the toxicity symptom is similar to that of the flower of P. cuspidatum. Therefore, my research was focused on extraction, separation, purification, structure identification and preliminary study the toxic mechanism by the bioactivity guiding method. In order to search for new natural active substances and novel leading compounds to prevention and poison L. sericata. It can provide the necessary theoretical foundation and effective technical support for the development and utilization of germicides botanical pesticides.1. Observation of the biological phenomena of the toxicity symptom of L. sericata on the flower of P. cuspidatumThrough on-site observation and experiment on the toxicity symptom of L. sericata on the flower of P. cuspidatum. Before the P. cuspidatum is not flowering, L. sericata shows no interest in them. But when the P. cuspidatum is flowering, P. Cuspidatum attract a large scale of L. sericatas by the volatile compounds of its flower, gathering from all directions in succession, and sucking on the flower head. After some time, L. sericatas were exciting, flying without aims, bumping disorderly, rubbing the front foot constantly, accompanying by salivating, convulsing and other symptoms. With the extension of the feeding time and increases of food consumption, L. sericatas were gradually to be suppressed and fly slowly, anesthesia, and eventually death. The curve of the toxicity of L. sericata on fresh flower was: Y=2.1534X-8.8414, the correlation coefficient r=0.9872, LT50=27.32h. 2. Chemical analysis of the L. sericata attractant volatile compounds of the flower of P. CuspidatumUnder the base of a comprehensive observation of phenomenon of the specific toxicity symptom of L. sericata, the feeding attractant volatile compounds of the P. Cuspidatum flower were investigated by Headspace Sampler GC/MS. Analyzed floral volatiles of P. Cuspidatum flower. Compounds were separated and determined from P. Cuspidatum, which amount to99.29%of the total volatiles.5compounds, including2-hyexenoic acid methyl ester, valerophenone,4-hexenoic acid methyl ester,3-hexenoic acid methyl ester,2-methyl-6-methylene-1and7-octadien-3-one, were the main constituents existed in P. Cuspidatum flower, which amount to63.23%of the total volatiles. From the perspective of the type of component, organic ester compounds amount to52.09%of the total volatiles. Among, hexenoic acid methyl ester compounds were most, which amount to85.66%of the total organic ester compounds. In addition, the valerophenone and acetophenone were16.30%and4.33%, which amount to20.63%of the total volatiles.3. Separation of insecticidal active substances from P. Cuspidatum flowerIn order to find and ascertain the insecticidal active ingredient of the flower of P. Cuspidatum on L. sericata, Insecticidal experiment of petroleum ether extract, ethyl ether extract, n-butanol extract, methanol extract and water extract of methanol extract of the flower of P. Cuspidatum were performed. The result indicated that the petroleum ether, ethyl ether and methanol extraction have good insecticidal activity, their LC50were1.31,0.30,0.64mg/mL, respectively. The insecticidal activity n-butanol and water extract was not detected. In order to further investigate the insecticidal active substances, the chemical composition of the petroleum ether, ethyl ether extract and methanol extract with stronger insecticidal activity was separated and isolated.7compounds were obtained from ethyl ether extract.22compounds were obtained from methanol extract. Among these compounds obtained, aloe-emodin, kaempferol, phloridzin, luteolin, hesperetin,4-hydroxyacetophenone, sucrose, genistein, hesperidin,(-)-epicatechin,1-(S)-phenylethyl β-D-glucopyranoside were first isolated from P. cuspidatum.4. Insecticidal activities of monomer compounds isolated from the flower of P. CuspidatumIn order to find the real insecticidal substance and lead compounds, insecticidal activity screening experiment of all of the compounds isolated were carried out. The study found that anthraquinone (aloe-emodin) compounds have good insecticidal activity, symptom of poisoning of insects by aloe-emodin was similar to that of extracts. The efficiencies of insecticidal active were increased as the reagent concentration of emodin, physcion, rhein, chrysophanol increases, and the knockdown rate of aloe-emodin was over50%. After10h, death number of L. sericata is increasing with the reagent concentration increase. The efficiencies of chrysophanol and aloe-emodin were more significant, and their death rate reached56.67%and86.67%, respectively. When the concentration of emodin, physcion, rhein, chrysophanol, aloe-emodin are3.75mg/mL, the death rates of L. sericata were43.33%,20.00%,30.00%,56.67%and86.67%at10h, respectively, and50.00%,30.00%,53.33%,70.00%,90.00%at20h, respectively.10h after the adult L. sericatas sucking the reagents of emodin, physcion, rhein, chrysophanol, aloe-emodin administration, the LC50values were3.74,5.90,4.89,3.06,2.44mg/mL, respectively.20h after the adult L. sericatas suck the reagents, the LC50values were3.36,5.29,3.17,1.90,2.26mg/mL, respectively.5. Mechanism of poisoning L. sericata on the anthraquinones from the flower of P. CuspidatumInsecticidal activities experiment indicated that anthraquinone is an important kind of insecticidal substances. Anthraquinones have obvious neural poisoning effective. It can be inferred from the symptom of poisoning of insects that anthraquinones were acting on the central nervous of L. sericata. At the stage of exciting period, the activity of the acetylcholin esterase of the reagents feeding group was lower than flower of P. Cuspidatum sucking group, namely, the enzymatic specific activity was reduced. The inhibition rate of the emodin, physcion, rhein, chrysophanol, aloe-emodin and fresh flower on the acetylcholin esterase were7.03%,8.59%,24.02%,11.13%,32.62%and36.13%, respectively. And the contents of neurotransmitter-acetylcholin esterase in the body of L. sericata were increasing rapidly at this stage. The results indicated that they were9.45,8.41,9.24,8.98and3.23times than the control group. This trend was consistent with the flower of P. Cuspidatum. Since the action of acetylcholin esterase was inhibited at the L. sericata exciting period, acetylcholine couldn’t be hydrolysis to acetic acid and choline. Eventually, the amount of acetylcholine accumulated and couldn’t stop the transmission of neural signal. Brain neuron was kept in continuously exciting state at this stage. L. sericatas were flying without aims, bumping disorderly, rubbing the front foot constantly, accompanying by salivating, convulsing and other symptoms. With the extension of the feeding time, food consumption increases, acetylcholin esterase activity increased resulting in acetylcholine hydrolysis rapidly. Insufficient release of acetylcholine makes the neurotransmission inhibited, L. sericatas turn the exciting period to inhibitory period (anesthesia period), they fly slowly, anesthesia, and eventually death. During the inhibitory period to the death, L. sericatas act slowly and clumsily, food consumption was further increased. Therefor, anthraquinones expresses rapid activation of acetylcholin esterase in the body of L. sericatas. At this period, the activities of acetylcholin esterase of emodin, physcion, rhein, chrysophanol, aloe-emodin treated group were2.42,2.37,2.53,2.44and4.02times than the control group. |
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