Isolation And Identification Of A Pathogenic Strain Of Locust And Its Toxicity

Locust is a kind of worldwide pest to crops and other plants. It can make large lose and grave treatment to agriculture.Chemical pesticide causes many problems while killing pest:environmental pollution,chemical resistance, breakdown ecological balance,etal.So,pest biocontrol acqure high reconstruction in the world because its merits. Nosema locustae is the first succefful pesticide using to control locusts in china. Beauveria bassiana, Metarhizium anisopliae,and Maxtrhizium flavoviride are insects' pathogenic fungus. They all have high toxicity to locusts. Pseudomonas pseudoalcaligenes and Bacillus cereus are insects' pathogenic bacteria They also have some toxicity to locusts. But the truth is ,until now, locust is still out of control. Finding out new pathogenic bacteria and developing high toxicity pesticide is still our top responsibility.A pathogen hb was isolated from naturally dead locust, denominate hb.The pathogenicity of hb was testified by law of KOCH. Using follow method to preserve this strain: glycerol quick freezing method and petroline slant tube method.Inorder to conform the function of this strain in biocontrol, we determinated the toxicity of the strain hb to the locust. It was assayed by the way of oral infection. The results showed that the strain hb had a strong toxicity to locust.The linear regression relationship between the logarithm(x) of hb concentration and the probability(y) of corrected locusts morality is:Y=1.1993X-9.745 and the median lethal concentration is:LC₅₀=1.33×10⁸cfu/mL, the correlation coefficient R=0.9158.Toxicity of hb to silkworm was also assayed by the way of oral infection. The results showed that the strain hb had no toxicity to silkworm.It is to say, Lepidoptera insects is out of the spectrum of this isolated strain.Inorder to identify the insect disinfestation material,we add proteinase K into fermentation broth of the isolated strain hb after centrifuging.Then spraying the broth onto corn seedling and feed it to locusts.The result showed that proteinase K inhibits the toxicity of strain hb obviously.So,we can initially preliminary determin the insect disinfestation material as a kind of extracellular protein produced by strain hb.The strain hb was identificated by molecular biology method 16SrDNA. Using GP primers of bacterium to PCR the conserved sequence of the strain and then link the conserved sequence and pTA2-T vector, transformate Escherichia coli DH5a.. Selecte the positive colony. Extract plasmid after 24h culture.Then the plasmid was sent to determining sequence after confirming by enzyme cutting. Based on the results of physiological and biochemical fertures, 16SrDNA sequence and DNA homology analysis, the strain hb was identified asAlcaligenes sp.