Studies On The Screening And Culture Condition Of High Virulent Strains Of Metarhizium Anisopliae

Metarhizium is one of the pioneers of insect-pathogenic fungi mass-produced and applied in the field control.Since 1878 Metschnikoff controlled Anisoplia austriaca and Cleonus punativentris using Metarhizium anisopliae,researchers have done lots of work and made a great progress especially in dosage form improvement and control object enlargement.However,we still have mass study to do compared with Bt.21 strains of Metarhizium were collected and their basic biology characters were studied.Four strains were selected according to the sporulation quantity as main index.Their virulence on several target pest was tested.The result showed that the virulence of these strains are varied.Among them,Metarhizium anisopliae₇₈₉(Ma₇₈₉) was the most virulent one.Liquid-shake culture and solid-plate culture of Ma₇₈₉was studied.Experiment of controlling Monochamus alternatus larva was done with Ma₇₈₉carried by Sxleroderma guani.The main results were as follows:1.According to the study on basic biological characters of 21 strains,there are lots of difference in colony growth rate,initial time of producing spore,sporulation, and heat resistance of spore.The maximum in sporulation of the best strain is 40 times more than the worst.Heat resistance of Metarhizium spore is also different. Testing for the germination percentage with different temperatures water bath treatment,the strain Ma₇₈₈showed the strongest on the heat resistance,the next were Ma₁ and Ma₄₂,the strains Ma₇₈₉was weakest.2.The virulence of different Metarhizium strains on Monochamus alternatus adults was tested by direct injection.The result showed that strain Ma₇₈₉was the most virulent one,the next was Ma₇₈₈,while strain Ma₄₂was the weakest.Virulent against Clostera anachoreta larvae of different Metarhizium strains was measured by food pollution method.The result showed that strain Ma₇₈₉was the most virulent one. The strain Ma₇₈₉also showed the highest virulence on Exolontha umbraculata larvae.3.The virulence of different strains(Ma₁,Ma₄₂,Ma₇₈₈,Ma₇₈₉,B_福建)on Monochamus alternatus larva was tested.The results showed that strain Ma₇₈₉was the most virulent one,and the LC₅₀on Monochamus alternatus larva was 2.9×10⁵ conidia per mL(C=10⁵～10⁸ conidia per mL).The results showed that the parasitical death rate of Sxleroderma guani on Monochamus alternatus larva rose with the increasing of inoculation with S.guani.The average corrected mortality was 96.7%(M.alternatus amount:S.guani amount=1:4～1:5).When every S.guani carried about 1.0×10⁷ conidia of Ma₇₈₉,and inoculated M.alternatus larva with 1:1,1:2 and 1:3,the ratios of M.alternatus amounts to S.guani amounts,the parastizing infecting death rates were 56.667%,70%,and 100%respectively.4.Conditions of liquid shake culture to Ma₇₈₉were studied using the orthogonal test.The optimum liquid medium recipe for mycelium culture was sucrose2.0%, yeast-extract paste1.0%,KH₂PO₄0.3%,MgSO₄·7H₂00.1%,CaCl₂0.05%.The optimum liquid medium recipe for the spore production was sucrose2.0%, peptone 1.0%,KH₂PO₄0.15%,MgSO₄·7H₂00.2%,CaCl₂0.05%.Moreover,the effect of mycelium growth and sporulation of Ma₇₈₉on different carbon sources were studied by plate culture.