Study On Screening And Cultural Condition Optimization For Pathogenic Fungi Against Longhorn Beetle

Longhorn beetle is regarded as a common pest for agriculture and forestry.The Monochamus alternatus is a main pest damaging the multiple kinds of pine trees which is also an essential vector insect for the Bursaphelenchus xylophilus that could cause the pine wilt disease which is also known as"pine cancer".The damages causing by the M.alternatus could be ended up with both great economic and ecological losses.While biocontrol methods using Beauveria sp.and Metarhizium sp.provided a new perspective for controlling the population of pest such as M.alternatus.Nevertheless,the pathogenicity could vary with the virulence differences of different strains,therefore,strain selecting and screening become the necessary key point during the utilization of entomopathogenic fungi.The main results conducted in this study were as follows:（1）The results of the strains selecting and identification:30 different strains were selected from the soil samples and identified by constructing the phylogenetic tree together with the comparison and observation of morphological characteristics including the Metarhizium anisopliae,Metarhizium robertsii,Metarhizium brunneum,Metarhizium lepidiotae,Beauveria bassiana and Isaria fumosorosea.（2）Virulence of the Beauveria sp.and Metarhizium sp.tested with Tenebrio molitor larvae:Virulence tests were conducted by using the Tenebrio molitor larvae.Ten strains with high virulence were selected in total.Virulence of the Beauveria sp.and Metarhizium sp.tested with M.alternatus larvae:After testing and screening with Tenebrio molitor larvae,ten strains mentioned below were tested with M.alternatus larvae with a concentration of 1×10⁸.Three strains with the most strong pathogenicity were finally selected following the LT₅₀value:CZA3-1（3.19 d）,FSL2-1（3.84 d）and XM1-3-1（4.28 d）.The LC₅₀of each is FSL2-1（3.96×10⁵spore/m L）,CZA3-1（1.96×10⁶spore/m L）and XM1-3-1（5.28×10⁶spore/m L）。（3）Virulence of the Beauveria sp.and Metarhizium sp.tested with M.alternatus larvae under the condition of different concentrations:Using five different concentration treats,related LT and LC value was concluded.（4）Histopathology of the M.alternatus infected by XM1-3-1,CZA3-1 and FSL2-1:By observing the tissue sections of the different periods or the stages of the infection,infection process was concluded.（5）The optimized culture conditions of three strains:The optimized carbon and nitrogen sources of medium for three strains were tested.According to the results,the pupa powder was better for carbon source of the media promoting the growth of mycelium and the D-sorbital was better for spore production as carbon source as well as yeast extract generally.Above all,these results indicated that the CZA3-1、FSL2-1 and XM1-3-1 had better capacity of pathogenicity to the M.alternatus according to the both virulence test and Histopathology which ensured that they had the potential value for furthering utilization of the biocontrol for M.alternatus and other beetles.