Studies On Prevention & Cure Technology Of Bacillus Thuringiensis Against Pieris Rapae

Bacillus thuringiensis (Bt) was isolated successfully by selective medium from subtropics yellow soil in Chengdu plain of Sichuan. It was named SC-1 and identified. The results proved that: it can produce a lot of parasporal crystal after 72h in BP medium. The size of crystal is 0.5~1.0 u m. Its shape is rhombus.Indoor bioassay was carried out about SC-1, kurstaki and kenyae against Lepidoptera insect-Pieris rapae larvae. Results of bioassay shows: Pieris papae larvae can be infected with 3 strains. But the toxicity is different. In the same concentration, the toxicity of kurstaki is the highest, kenyae is lower than kurstaki and SC-1 is the lowest. At the same time, the toxicity will be enhanced with the increase of concentration, whose rule of enhancement can be expressed by the linear regression equation. In different culture condition, the toxicity is not same. 3 strains of Bt were respectively cultured by LB and improved medium. Then bioassay proved: toxicity of the same strain cultured by improved medium is 1.3 times higher than the one cultured by LB medium.Pieris rapae larvae can be infected with Nosema bombycis (Nb). The Bt and Nb were mixed and used. The results proved: the death rate of Pieris rapae larvae was obviously improved compared with separate use of them.Crystal protein of 3 strains Bt was purified and analized with SDS-PAGE. The results demonstrated that: 130~140 kD protein was produced by kurstaki, which hashigh toxicity against Lepidoptera pest. Kneyae and SC-1 can produce 71kD crystal protein, the kind of protein also has toxicity against Lepidoptera pest.