The bacterium Bacillus thuringiensis (Bt) is characterized by its ability to produce proteic crystalline inclusions during sporulation. Cry1 protein has insecticidal activity and is highly specific to certain insects and not toxic to unrelated insects, plants or vertebrates. In this work, the patogenicity of twelve Bt isolates was tested against Anticarsia gemmatalis, one of the most important insect pests of soybeans. Spore-crystal complex was applied to the surface of artificial diets and the mortality of A. gemmatalis larvae was assessed seven days after each treatment. When compared to a control Bt isolate known by its high toxicity to A. gemmatalis larvae, four novel Bt isolates exhibited even higher toxic activities against the insect, resulting in more than 90% mortality. PCR was used to amplify DNA fragments related to known cry1 genes. Bt strains with high toxicity produced expected PCR products of around 280 bp, whereas non-toxic or low toxic strains did not produce any PCR product or showed amplified fragments of different sizes. Toxic Bt isolates also exhibited an expected protein profile when total protein extracts were evaluated by SDS-PAGE.
Bacillus thuringiensis; velvetbean caterpillar; Anticarsia gemmatalis; cry1 gene; delta-endotoxin