Study On Characterization And Wettable Powders Of Bacillus Thuringiensis MB-15 Strain

Bacillus thuringiensis MB-15 (Bt MB-15) with high insecticidal activities against Lepidoptera vegetable pests was isolated from soil in Hebei province. In order to make further evaluation on the potential of Bt MB-15 as microbial insecticide, the crystal shape, protein type, genotype, growth characteristics and toxicities of Bt MB-15 were observed and analyzed. In addition, the wettable powder of Bt MB-15 was developed by using its mixture of spore and parasporal crystals. The results were as the followings.1. The bioassay results indicated that the toxicities of Bt MB-15 against Helicoverpa armigera, Spodoptera exigua, Plutella xylostella, Spodoptera litura and Pieris rapae all were higher than that of Bt HD-1.The supernatant of Bt MB-15 fermentation could enhance remarkably the insecticidal activity of mixture of spore and parasporal crystals of Bt MB-15. Bt MB-15 could produce the bipyramidal crystals during sporulation phase of growth. SDS-PAGE analysis revealed that Bt MB-15 produced crystal proteins of 130.0kD and 65.0kD.PCR-RFLP analysis showed that Bt MB-15 contained cry1Ac, cry2Aa, cry1I and vip3Aa genes. These results suggested that Bt MB-15 may have good potential to develope the microbial insecticide for controlling Lepidoptera vegetable pests.2. In order to develop the formulation of Bt MB-15 wettable powder, the carriers, wetting agents, dispersers, stabilizers and ultraviolet protectors were screened. The optimal formulation was obtained by using the freeze dried powder of the mixture of spore and parasporal crystals from Bt MB-15 as raw material. The ingredients of the Bt MB-15 wettable powder formulation were confirmed as follows: 50.0% Bt MB-15 bacterium powder, 10.0% Dodecyl Benzenesulfonate as wetting agent, 5.0% Sodium Sulphonate Lignin as disperser, 1.0% Xanthan Gum as stabilizer, 1.0% skimmed milk powder as ultraviolet protectant, 33.0% White Carbon Black as carrier. The quality detection showed that the content of toxin protein, titer, suspension and wetting time were respectively 2.4%, 26546IU/mg, 74% and 123s, which accorded with formulation standard of the GB/T 19567.3-2004 about B. thuringiensis wettable powder. The result of potting experiment showed that Bt MB-15 wettable powder had similar control effect with commercial Bt agent. 3. The synergistic effect of Bt MB-15 mixtured with six additives on 2rd-instar larvae of P. xylostella were respectively determined and evaluated by the leaf dipping method in laboratory. The results showed that the mixtures of Bt MB-15 with 0.1% ZnCl2, 0.5% ZnCl2, 1.0% ZnCl2, 1.0% MgCl2, 0.5% Boric Acid, 1.0% Boric Acid, 0.5% Citric Acid and 1.0% Citric Acid all had synergistic effect, in which synergistic effect of 0.5% Boric Acid was the highest with 17.2 synergistic ratios, and the next was 1.0% ZnCl2 with 15.6 synergistic ratios. Meanwhile, the influences of 0.5% Boric acid and 1.0%ZnCl2 to insecticidal speed of Bt MB-15 were measured. The results indicated that the addition of 0.5% Boric Acid could make the LT50 of Bt MB-15 wettable powder to shorten about 10 hour. After the mixtures of Bt MB-15 with 0.5% Boracic acid or 1.0%ZnCl2 was stored for 15 days at room temperature, the toxicities of two mixtures did not have significant change.