Study On The Compatibility Of Entomogenous Fungi Of Monochamus Alternatus With Dastarcus Helophoroides (Fairmaire)

Monochamus alternatus Hope is the main insect pest of pine trees.And it is also the most important vector insect of pine wood nematode disease known as"cancer"of pine trees.It has now been included in the"List of Forestry Hazardous Organisms".Beauveria bassiana and Dastarcus helophoroides(Fairmaire)are very important biocontrol agents to control Monochamus alternatus and have been widely used in practice.However,whether B.bassiaia has virulence to Dastarcus helophoroides(Fairmaire)and the compatibility between the two agents remain unknown.The purpose of this study is to screen strains with high virulence against Monochamus alternatus;Meanwhile,the compatibility of B.bassiaia and Dastarcus helophoroides(Fairmaire)was studied so as to provide relevant theoretical basis for the joint control of Monochamus alternatus.The main research results of the paper:Morphological and molecular identification of Beauveria bassiana strains.Strains Bb3275,Bb3276 and Bb3277 were isolated and purified from wild plants and infected with B.bassiaia.The spore morphological characteristics of the observed strains were single cells and the spores were nearly spherical in size and ranged in size from 1.5~2.8×1.5~2.4?m.According to morphological identification and the ITS sequence analysis,it was confirmed that all the four tested strains were B.bassiaia.Biological characteristics of the tested strains.The strains Bb202,Bb3275,Bb3276and Bb3277 were tested for strain morphology,colony morphology,spore formation,germination rate and growth rate.Excellent strains Bb3275 and Bb202 with good biological properties were selected.The results showed that the colony surface of the strains Bb202 and Bb3275 was thin and powdery.The colony of strain Bb202 was yellow,while the colonies of strains Bb3275,Bb3276,Bb3277 were white.The back of the substrates of strains Bb202 and Bb3275 is yellow,and the back of the substrates of strains Bb3276 and Bb3277 is light yellow.The sporulation results of the strains showed that:Bb3275>Bb202>Bb3277>Bb3276.From the largest to the smallest,they were1.65×10~7/cm~2,1.33×10~7/cm~2,0.95×10~7/cm~2,and 0.9×10~7/cm~2.The order of spore germination rate of spore germinating strains of the tested strains was Bb3275>Bb202>Bb3277>Bb3276.The colony diameters of strains Bb202,Bb3275,Bb3276,Bb3277cultured on PDA medium on the 14th day were 52.10 mm,53.15 mm,50.15 mm,and50.31 mm.Determination of the pathogenicity of Beauveria bassiana to Monochamus alternatus.Using the dipping method,the pathogenicity of the two strains Bb202 and Bb3275 with good biological properties on different insect instars of Monochamus alternatus was determined.The results showed that the two strains exhibited strong virulence to larvae and adults of Monochamus alternatus,and the pathogenicity of Bb3275 was slightly higher than that of Bb202.The concentration of spore suspension of each strain was positively correlated with the cumulative mortality rate of Monochamus alternatus.At the concentration of 1×10~8 spores/ml,the corrected mortality rates of Bb3275 and Bb 202 to Monochamus alternatus were over 80%.Among them,the pathogenicity of B.bassiaia to the adult Monochamus alternatus is higher than that of larvae.The corrected mortality rates of strain Bb3275 to adults of Monochamus alternatus at four different concentrations were 95.45%,81.82%,50.51%,and 31.82%respectively.And the infection rate were 91.67%,70.83%,41.67%,29.17%.The corrected mortality rates of Bb202 to adults of Monochamus alternatus were 90.91%,77.28%,50.01%,and 27.27%,and the infection rates were 83.33%,66.67%,37.50%,and 16.67%,respectively.Determination of the pathogenicity of B.bassiaia to Dastarcus helophoroides(Fairmaire).The pathogenicity of the strains Bb202 and Bb3275 to the larvae and adult of the Dastarcus helophoroides(Fairmaire)was measured.Results showed that only the treatment with 1 x 10~8 spores/ml(the highest concentration)of spore suspension caused the death of Dastarcus helophoroides(Fairmaire).The corrected mortality rates of the strains Bb3275 and Bb202 to the larvae were 13.64%and 9.10%,and the mortality rate for the adult of the Dastarcus helophoroides(Fairmaire)was 9.10%and 4.55%.The infection rates of the two strains on both larvae and adults were both 0.00%.Thus,we can conclude that the pathogenicity of B.bassiaia is extremely low on Pinus armandi,and B.bassiaia has certain compatibility with Pinus armor.Analysis of the infection of Dastarcus helophoroides(Fairmaire)by Beauveria bassiana under simulated conditions.The Monochamus alternatus larvae were dipped in spores suspension of B.bassiaia,and then put in the same environment with Dastarcus helophoroides(Fairmaire)larvae.Results showed that the corrected mortality rate of Monochamusalternatuswas86.96%~82.60%,andtheinfectionratewas83.33%~70.83%.However,the corrected mortality rate for flower armour is9.10%~0.00%and the infection rate is 0.00%.Our study suggested that Dastarcus helophoroides(Fairmaire)has good compatibility with B.bassiaia.Simultaneous application could be adopted when controlling Monochamus alternatus in field.