Bacillus thuringiensis is well known for its ability to produce toxic proteins to different insect orders which are encoded by the cry genes. This work was carried out aiming to select among different B. thuringiensis isolates, by morphological and molecular characterization, identifying different classes of cry3 and cry35 genes, and to determine the level of pathogenicity against Sphenophorus levis larvae, which is one of the most important sugar-cane pests in Brazil. A total of 1163 bacterial isolates were used in this survey in which phase microscopy and molecular markers were used for evaluation that resulted in 30 isolates positive for cry3 and cry35 genes potentially active against coleopterans. These bacterial isolates together with type strains such as B. thuringiensis var. tenebrionis, B.t. var. morrissone e B.t. var. tolworthi were used in bioassays using Sphenophorus levis larvae. Using discriminating analysis four groups of isolates were produced when B. thuringiensis toxicity was taken into account. These groups involved one set of two isolates with up to 10% mortality; another set caused mortality of up to 39% and was made up of ten isolates and three type strains; another set caused mortality of up to 52% containing thirteen isolates and a last set of isolated whose mortality index was 70% containing only five isolates which were considered promising bacterial strains for biological control of S. levis.
PCR; bioassay; biological control
