The Study On Screening And Inducing Of Entomogenous Fungi Strains

Scolytus schevyrewi Seme and Holcocerus vicarious Walker are two severe kinds of the wood-boring pests in damaging the elm. Except for the insect pheromone trap and kill, there are no other means of control which are convenient and effective. However, it was recently reported in the literature that the combination of insect pheromones and entomogenous fungi has been adopted in wood-boring pests prevention and control. This new biocontrol mode is particularly cost-effective. And in applying the biocontrol mode, the first step is then to Screen the high virulent strains up to the standards.This study screened5strains by testing their biological activity in pathogenicity for larvae of Scolytus schevyrewi Seme and Holcocerus vicarius Walker. The strains Bb773and Pc546are the highest in the test. Based on the statistical analysis of colony count (Colony Forming Unit), the best selective medium is chosen which is:cupric sulfate0.1g, rose bengal sodium salt0.033g, chloramphenicol0.2g, cycloheximide0.2g, oatmeal40g, extract of bombyx batryticatus100mL, agar28g, add water to1000ml, nature pH. Screening was carried out by using the plate assay and the enzyme activity was detected by using folin-phenol method and DMAB method, in which continuous cultures were conducted and the time for the maximum activity of the strains’ chitinase and protease was also tested. The results showed that chitinase activity of the strain Bb773and Pc546reached the peak after4days and6days respectively and protease activity of the strain Bb773and Pc546reached the peak after2days and10days respectively. It showed that there was a significant correlation between the activity of FDA hydrolysis and the activities of chitinase, but insignificant with protease, under the same experimental conditions by strains Bb773and Pc546, which provide the basis for enzyme activity determination in the strains screening process and support for the FDA hydrolase activities used as a rapid screening method. The best dosage of mutagen and mutagenesis time were decided respectively through statistical CFU. The results showed that:on the basis of the lethality rate, the use of20μL diluent diethyl sulfate (DES) in treating single spore suspension for90minutes and of30μL diluent diethyl sulfate (DES) in treating it for10minutes. The sporulation quantity of strains Bb773and Pc546were found declining over continous3passages on culture medium.