Bacillus thuringiensis strains to control Noctuidae pests

Abstract

This study aimed to select and characterize Bacillus thuringiensis strains with toxic activity on Helicoverpa armigera, Spodoptera cosmioides and Spodoptera eridania. Fifty B. thuringiensis (Bt) strains were used in selective bioassays for high mortality on H. armigera, and the four most efficient strains were tested on S. cosmioides and S. eridania. Twelve Bt strains were characterized by PCR to detect some cry, cyt and vip genes. Bioassays were also performed to detect the production of β-exotoxins. Strain 237 caused a mortality rate of 95.6% due to β-exotoxins. Strains 1368, 1521, 1814 and 3299 showed toxic activity on S. eridania. However, no strain was effective on S. cosmioides. The presence of β-exotoxin was detected only in strain 237. The molecular characterization of the strains using specific cry, cyt and vip primers showed a great genetic diversity among the 12 strains that showed some mortality on H. armigera and S. eridania. Our results showed that detecting β-exotoxin in Bt strains is important as it is toxic to insects and vertebrates and persistent in the environment. Strains 1368, 1521, 1814 and 3299 did not show toxicity to H. armigera, while they were toxic to S. eridania and did not produce β-exotoxin. These strains may be useful for new formulations of biopesticides as well as for cloning and expression of plants' genes.