A Screening And Identification Of Tobacco A High Virulence Of Bacillus Thuringiensis

Lasioderma serricorne is an important storage pest in the world. The loss caused by the pest over one hundred million dollars in the world each year. Conventional control methods have not resistance to them, and pullute the environment.Bacillus thuringiensis is a wide range of microbial pesticide in application which has a significant effect. From the nineties of the last century, scholars all over the world have begin to the research of the control of Bt to Lasioderma serricorne.In our research, 19 strains of Bacillus thurigiensis containing parasporal crystals were isolated among 258 samples collected from soil, tobacco and plant leaves by Sodium Acetate method.The form of parasporal crystals are diamond mainly and rectangle seldom.The tatol relevance ratio is 7.36%.In these materials, the relevance ratio of tobacco is 13.33% which is the highest in all samples. It shows tobacco is an important habitat for Bt.Under the conditions of 30℃, RH75%, using artifical feed(corn flour and yeast extract mixed completely in 10:1),larvae of the cigarette beetle were raised successfully. The result show nutrient content and physical behavior in feed may be work upon the growth of Lasioderma serricorne to some extent.19 Bt strains were tested for their insecticidal activity against larvae of the cigarette beetle raised.There were 6 Bt strains appeared high toxicity against larvae of the cigarette beetle in primary screening. The number is 115,106,119,117,121,207respectively.The corrected mortality in tenth day is 48.28%,55.17%,58.82%,68.97%,51.73%与48.28% respectively. After secondary screening, The corrected mortality in 12th day is 48.28%,51.73%,58.62%,72.41%,51.73%,44.83% respectively. The LC₅₀ value is 43.89057,42.60283,38.64439,29.02226,43.72312,52.42485mg/L respectively. Bt117 was sure of the most high toxicity against larvae of the cigarette beetle, which is the strain researcher wanted.According to identification of morphological, physiological and biochemical characteristics, 16S rDNA sequences, Bt117 belongs to Bacillus thuringiensis.Because the sequencing result of Bt117 strain resembles some sequencing models of Bacillus thuringiensis,Such as Bacillus thuringiensis strain 2000031482,which similarity is 99%. The shape of trophosome is rhabditiform, the shape of crystal is diamond.Colony is disc-shaped,milky white and full of wrinkles in surface. Physiological and biochemical characters of the strain Bt117 is in accord with the characters of Bacillus thuringiensis.