The Screening And Optimization Of An Effective Beauveria Bassiana Strain Against Asian Corn Borer

The Asian corn borer(Ostrinia furnacalis),a major pest of corn in China,has caused a great loss to maize production.The entomopathogenic fungus Beauveria bassiana has been considered to be one of the most important and promising biocontrol agents of natural pathogens against the Asian corn borer.The use of B.bassiana against Asian corn borer had been promoted by China's agricultural sectors in the northeast area since the mid 1970s.Now the technology has become one of the important means of prevention and control of corn borer in Northeast China.Although the application of B.bassiana is widespread,it is common that the degeneration of the bacterial strains and the unstable control effect during application and conservation,which limits the widespread promotion of B.bassiana in controlling corn borer.Therefore,it seems crucial to screen out an efficient and advantageous B.bassiana strain forcorn borer control.From the main corn planting area in Anhui,we sampled the B.bassiana and then cultured it in the lab.We screened out one promising B.bassiana strain,and then test its field and indoors effective on corn borer,and finally optimized the its specific culture conditions.We screened out six strains of B.bassiana from the samples collected from Dongzhi County,Chizhou City;Feidong county,Hefei City;Changfeng County,Hefei City;Dingyuan County,Chuzhou City;Fengyang County,Chuzhou City and Xiao County,Suzhou City,Anhui province.Through the experiment of the sporulation,germination rate,growth rate,resistance test and bioassay on two instar larvae of Asian corn borer in the laboratory,we screened out the strain Bb003 collected from Changfeng County,Hefei City,which featured by sporulation and germination rate reached 2.25*10~8per/cm~2 and 96.81%respectively.The lethality rate of multiple-strains to two instar larvae remains unchangeable after a 10-day indoor experiment We found that the accumulative correction mortality rate of all B.bassiana strains to corn borer larvae,is between 58.76%?95.88%,of which Bb003 strain has the highest correction mortality of 95.88%.We found that,comparing with chemical pesticide phoxim granules in the field experiment,strain Bb003 demonstrated the relatively lower control efficiency and the reduction of the second generation of B.bassiana individuals than75.56%and 81.30%of chemical pesticide respectively.However,both the control efficiency and the reduction of the third generation B.bassiana were all superior to phoxim granules at 29.88%and 24.20%respectively.Our experiment on the effect of various conditions such as the incubation time of nutrients medium,temperature,initial pH value,nitrogen source and carbon source,turned out that strains reached at the maximxum growth rate at the 12th day,and bacterial strain grows fastest and has highest sporulation quantity at 25? and alkalescen.After synthesizing the various biological traits of fungi,our results implied that glucose and peptone are the optimal nitrogen source and carbon source for sporulation and colony growth.