Screening Of Bt Toxins With High Toxicity Against Athetis Lepigone And Action Mechanisim Of Bt Toxins

In order to screen high virulence toxin to the larvae of Athetis lepigone Moschler, the insecticidal activities of five Bacillus thuringiensis(Bt) strains and four kinds of Bt toxins(Cry1Ac, Cry1 Ab, Cry2 Ab and Vip3A) were evaluated by using bioassay method. The genotype of these strains were analyzed. Strains Bt SC-40 and Bt HD-73 showed high insecticidal activity. The insecticidal activities of 2 kinds of Bt toxin(Cry1Ac and Cry1Ab) were highest with 82.9% and 79.2% corrected mortality against the 2th instar larvae of A. lepigone at 72 h, Vip3 A toxin also had insecticidal effect with 50% mortality. The insecticidal activity of Cry2 Ab was the lowest.The LC50 of Cry1 Ab and Cry1 Ac to 2th instar larvae were 0.89μg/g and 1.22μg/g repectively.In order to understand the site of action of Bt toxins, the BBMV(brush border membrane vesicles) protein had been extracted from the 4th instar larvae midguts of A. lepigone. The dot blotting experiments of BBMV proteins with antibody of Cry1 Ac or Cry1 Ab confirmed that the action site of Cry1 Ac and Cry1 Ab all were on midgut BBMV. The receptor protein of Cry1 Ac on BBMV was identified as aminopeptidase N(APN) by ligand blotting and matrix assisted laser desorption-time of flight-mass spectrometry.The transmission electron microscope(TEM) had been used to observe the cell pathological changes in the larval midgut of A. lepigone who fed on an artificial diet mixed with four different kinds of Bt toxins respectively. The results showed that the cell pathological changes of the larva midguts of A. lepigone were positive correlations with toxicity of Bt toxins. The cell pathological changes of larval midguts in A. lepigone caused by Cry1 Ac and Cry1 Ab were more severe than that by Vip3 A and Cry2 Ab.