Selection and characterization of Bacillus thuringiensis efficient strains against Diatraea saccharalis (Lepidoptera: Crambidae)

Abstract

The objective of this work was to select and characterize native strains of Bacillus thuringiensis toxic to Diatraea saccharalis (Lepidoptera: Crambidae). A hundred‑and‑six strains, belonging to the bank of invertebrate bacteria (Brazil), of Embrapa Genetic Resources and Biotechnology, were tested as to their toxicity to D. saccharalis, and the most toxic ones were characterized by biochemical and molecular methods. Out of the 106 tested strains, 16 caused 100% mortality within 24 hours. The three most toxic strains showed median lethal concentrations between 8 and 43 ng cm^-2. The protein profile of the 16 strains showed the presence of 130 and 65 kDa proteins, and the molecular characterization showed the presence of cry1 and cry2 type genes: cry1Aa, cry1Ab, cry1Ac, and cry2Aa. The median lethal concentration of spores and crystals obtained from recombinant strains, which individually expressed the genes cry1Aa, cry1Ab, cry1Ac, and cry2Aa, varied between 222 and 610 ng cm^-2, values much higher than the ones of the most toxic native strains, which have the possibility of simultaneously expressing these genes. This result indicates a synergy between the toxins. There are interactions between B. thuringiensis toxins and their receptors in the sugarcane borer.