Screening?bioassay And Control Effect On The High Toxicity Of Bacillus Thuringiensis In Soil Around Changbai Mountain Area

18 strains of Bacillus thuringiensis were isolated from the Changbai Mountain Area of 150 soil samples,the mountainous region separation rate was 8.5%,farmland separation rate was 16.2%.Through microscopic examination,the 18 strains produced with the spore crystal were all.Preliminary bioassay results showed that there were 17,5 and 4 among of 18 strains of Bacillus thuringiensis against Plutella xylosrella,Spodoptera exigua and Spodoptera litura whose mortality was over 90%.Four kinds of isolates showed with highly toxicity to Spodptera exigua,they were YN1-1,YN2-6,YN4-2,YN6-2.Further bioassay,Mortality rate reached 100 percent when the concentration was 1 x 106 cfu/ml,the median lethal concentration and lethal concentration were respectivelyl.57 x 105 cfu/ml ml and 2.43 x 106 cfu/ml,1.34 x 106 cfu/ml and7.44 x 106 cfu/ml,5.23 x 105 cfu/ml and3.26 x 106 cfu/ml,3.07 x 104 cfu/ml and 2.62 x 105 cfu/ml,control effect from big to small was YN1-1 YN6-2,YN4-2,YN2-6.Five kinds of isolates showed with highly toxicity to Spodoptera litura,they were YN1-1,YN2-1,YN4-1,YN4-4,YN6-1.Further bioassay,Mortality rate reached 100 percent when the concentration was 1 x 107 cfu/ml,the median lethal concentration and lethal concentration were respectively 3.31 x 105 cfu/ml and 9.74 x 105 cfu/ml,8.83 x 105 cfu/ml and 2.71 x 106 cfu/ml,6.25 x 105 cfu/ml and 1.79 x 106 cfu/ml,1.83 x 105 cfu/ml and 6.04 x 105 cfu/ml,2.8 x 105 cfu/ml and 1.17 x 106 cfu/ml,control effect from big to small was YN4-4>YN1-1>>YN6-1 YN4-1>YN2-1.After bioassay and toxicity determination,eventually YN1-1 was screened because of high activity as the target strains for protein insecticidal properties investigation.Its original toxin protein molecular weight was 136 kDa,and active protein molecular weight was 63 kDa.Adding a certain concentration of surfactant to liquid Bt,surveying the safety of crops and Bt and Bt deposition amount of foliage after spraying.The results showed that four kinds of surfactants are safety on Bt and vegetables.Speed,Organic silicon and Tween 80 3000 times diluent on the ten kinds of vegetables such as Onions can significantly increase the adhesion of Bt.This study selected YN1-1 strain.when handling Plutella xylosrella indoors,the second day efficacy reached 100%,was better than has been the commercialization of Bt(WP)efficacy.When dealing with Pieri s rapae and Spodoptera exigua,YN1-1 strain of efficacy was better than Bt(WP),but did not reach significant level.On the field control effect,YN1-1 strain of population decline rate is higher than Bt(WP),showed a good development potential.