Studies On The Insecticided Activity Secondary Chemicals Of Tropical Plant

To obtain plant secondary chemicals with insecticide properities and make use of them by producing botanic insecticides directly or taking them as template for composition of compounds with bioactivities is the aim of plant insecticide research. A study focusing on the screening out of secondary chemicals with bioactivities extracted from 50 species of tropical plants belonging to 26 families against Spodoptera litura , Brontispa longissima and Oligonychus biharensis was conduct in Danzhou, Hainan. Piper betle which the extraction with the highest bioactivities judged by preliminary tested results was chosen to make further extraction using various impregnants with different polarities. The antfeeding bioactivities and contact toxicity of the extractions to Spodoptera litura etc. were tested. The results indicated:1) The results of bioactivity test indicate that crude extracts from 7 species of plants possessed antifeedant rate beyond 50 percent to Spodoptera litura, of which the alcohol crude extract of Piper betle roots is the best, with an antifeedant rate of 92.50% on 4th larvae of Spodoptera litura after treatment 24h at the dose of 5 percent alcohol crude extract. And only the alcohol crude extracts of Piper betle roots have contact toxicity to Spodoptera litura , the mortality on the 4th larvaes of Spodoptera litura reached 100 percent after treatment 24h at a concentration of 5 percent of the alcohol crude extract. The alcohol crude extracts had good effects against the Brontispa longissima adults and larvae. There were 5 and 11 crude extracts showed mortalities beyond 50 percent on Brontispa longissima adults and larvae respectively at the concentration of 5 percent .Studies showed that 25 alcohol crude extracts had repellent activities against Oligonychus biharensis adults at the concentration of 5 percent, of which 20 extracts possessed high repellent rates (beyond 80 percent) to adult inhabitation and 21 extracts presented high repellent rates to oviposition (above 90 percent), of which the crude extracts from Melodinus suaveolens, Helicteres angustifolia, Datura metel reached 100 percent.2)The bioactivity of the extracts from the roots, stems and leaves of Piper betle repectively with petroleum ether, chloroform, ethyl acetate, alcohol, methanol by Sohxlet method were tested respectively. The results showed that the bioacticity of them are different with different parts of plant samples, the roots of Piper betle was the maximal, stems secondly, and leaves lastly. Bioactivity of the extract with petroleum ether was the highest. The results of antifeeding test showed that, non-selective AFC50 to Spodoptera litura 4th larvae of the extract with petroleum ether, chloroform from roots and the extract with petroleum ether from stems of Piper betle were 0.52%, 3.77%, 0.95%, and the selective AFC50 were 0.35%. 3.55%. 0.35%. The results of Bioassay Test showed that, the contact toxicities of the crude extracts against Spodoptera litura increased with the decrease of ages of the insects. The LC50 of the extracts with petroleum ether from roots and from the stems of Piper betle against Spodoptera litura 3th, 4th, 5th, 6th larvae were...