| A pathogenetic bacteria Bt-S04 was separated from the natural death larvae of Dendrolimus superans in Dayao of Huhhot. Morphology observation and the experiment of physiological and biochemistry reactions and culture characteristic of the bacteria was compared with the Bt-k01 strain.Its arginase reaction, urease reaction and salicin reaction were the negative, the velum reaction and the sucrose fermentation response were the positive. Its physiology biochemistry reaction characteristic was different from B.t.subsp.dendrolimus.The toxicity of two strains of Bacillus thuringiensis to the 2nd-instar larvae of D. superans fed on the host plant was examined in laboratory. The results show that LC50 of Bt-S04 and Bt-k01 to the 2nd-instar larvae were 5.493×106 CFU/mL and 7.227×105 CFU/mL,respectively. LT50 of Bt-S04 and Bt-k01 were:6.094 d and 1.216 d, respectively. The toxicity of Bt-k01 to the 2nd-instar larvae of D. superans was 7.6 times high than that of Bt-S04, LT50 of Bt-k01 was 1/5 of the Bt-S04 strain,Bt-k01 stain had more virulent lethal effect to 2 nd-instar larvae of D. superans fed on the host plant than Bt-S04.Due to Bacillus thuringiensis biologic activity and their poor power in preventing from ultraviolet, manufactured the Bt microcapsule, and analysis the anti-ultraviolet ability of this microcapsule and compared insecticidal activity of two Bacillus thuringiensis microcapsule by the toxicity determination method.After two hours exposured to ultraviolet, the survival rate of Bt-k01 and Bt-S04 were: 5.4% and 8.2%,respectively,but survival rate of microcapsule of Bt-k01 and the Bt-S04 were:72.0% and 76.3% respectively,indicating that microcapsule could enhance the ability of anti-ultraviolet of the two stain of bacteria. At the same time, the toxicity of Bt-k01and Bt-S04 microcapsule were determined, after two hours shinning of ultraviolet, the 2nd instar larva of Dendrolimus superans is 5 days mortality rate has achieved 78.3% and 68.3%, respectively.
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