Abstract: Insecticidal active substance of the fruiting body of Paecilomyces Cicadae（Miquel）Samson was isolated and purified by combined with separation and analyzing and biology experiment for the first time. The results showed that the water portion of ethanol-H20 total extract was strong toxicity to against the third instar larvae of Plutella xylostella L. in 24h, 48h and 72h with the corrective mortality of 46.67±1.34%、60±2.24% and 66.67±1.79%, respectively, at the concentration of 50.0mg/ml, and the other fractions of CH2Cl2, ethyl acetate and n-butanol were weak. By means of bioactive guided isolation of macroporous adsorption resin column, high performance liquid chromatography and sephadex A-20 column, a white powder compound was obtained. At the concentration of 10.0mg/ml, the corrective mortality of the compound against Plutella xylostella L were significantly ( P < 0101), 95.12±1.83%, 97.67±1.60% and 99.06±1.68%, respectively, in 24h, 48h and 72h. The bioactive compound was stable to acids and was not sensitive to proteinase pepsin, other physical and chemical chractristics were reported.

Key words: Paecilomyces Cicadae（Miquel）Samson, Plutella xylostella L, metabolite, Extract, Insectisidal activity