Characterization and selection of Bacillus thuringiensis isolates effective against Sitophilus oryzae

Abstract

The entomopathogenic bacterium Bacillus thuringiensis is a control agent with toxic and environmental characteristics that allows the control of pest insects according to the Integrate Pest Management (IPM) precepts. In order to find new strains, potentially toxic to Sitophilus oryzae L. 1763 (Coleoptera: Curculinidae), 1.073 strains of B. thuringiensis from parts of Brazil were used. Genetic material was extracted with InstaGene Matrix kit, used for the amplification of sequences in Polymerase chain reaction (PCR), and viewed in 1.5% agarose gel. The gene cry35Ba class was represented by 60 B. thuringiensis isolates (5.6%), which were then subjected to bioassays with S. oryzae larvae. Among the isolates studied, four caused more than 50% mortality in pathogenicity tests, and the isolates 544 and 622 were the most virulent, as determined by CL50 estimates. The four toxic isolates had spherical, bi-pyramidal and cuboid crystals, and a 44-kDa protein was found in sodium dodecyl sulphate - polyacrylamide gel electrophoresis (SDS-PAGE), which coded for the product of cry35Ba genes. These data demonstrate the potential of B. thuringiensis for the management of S. oryzae larvae.