Study On The Resistance Of Bacillus Thuringiensis To Batocera Horsfieldi (Hope)

Bacillus thuringiensis (Bt) could be used to prevent and control the damage of several Coleoptera insect pests. In order to obtain a highly toxic strain on Cerambycidae pest Batocera horsfieldi (Hope), resistance of 504 strains to B. horsfieldi have been detected, and the resistance mechanism was researched. The main results of this work as following:(1) Screening highly toxic strain. Through once primary screening and twice secondary screenings, ZQ-89 strain was found with the most powerful resistance to B. horsfieldi adults. Twenty days after infected, the rectified death rate of adults was 55.33%, the rectified rate of reduction in weight was 2.22% and the rate of reduction in hatching eggs was 19.62%. It was indicated that ZQ-89 strain had high resistance to B. horsfieldi adults and could inhibit adults in growth and hatching eggs.(2) The preliminary research about resistance mechanism of ZQ-89 to B. horsfieldi. FZQ-89 strain had been isolated from intestinal tract of dead B. horsfieldi infected ZQ-89. FZQ-89 was similar with ZQ-89 in morphologic characteristics, resistance activity and 16SrDNA identification. It was speculated that B. thuringiensis could play its resistance to B. horsfieldi after infecting insect intestinal tracts.(3) Research of active anti-insect components of ZQ-89. The pure crystal protein had the highest resistance to B. horsfieldi adults, so it was speculated that the crystal protein of ZQ-89 had played an important role in resistance to adults. Through detecting the resistance activity of different concentrations crystal protein, the median lethal concentration (LC50) was calculated as 21.961 mg/mL.(4) Cloning and analzing of resistance gene of ZQ-89 strain. ZQ-89 crystal protein had high homology with Cry1Ac proteins of B. thuringiensis. The primers were designed according to homology proteins, and the crylAc-89 gene was cloned. It has 3 534 bp and encoded 1177 amino acids.(5) Constructing engineered bacteria ZAC-89. The crylAc-89 gene was inserted into pHT304 vector, and then transformed into non-crystal mutant BMB171. The positive transformants was named ZAC-89. The crystals shape and protein molecular weight of ZAC-89 were similar with ZQ-89, the crystals were rhombic and the proteins were 133 kDa. It was speculated that ZAC-89 could play the same role in controlling insect pests and make a valuable contribution to forest protection.