SCREENING OF BACILLUS THURINGIENSIS ISOLATES PATHOGENIC TO SPODOPTERA FRUGIPERDA (J.E. SMITH) (LEPIDOPTERA: NOCTUIDAE)

SELEÇÃO DE ISOLADOS DE BACILLUS THURINGIENSIS PATOGÊNICOS PARA SPODOPTERA FRUGIPERDA (J.E. SMITH) (LEPIDOPTERA: NOCTUIDAE)

ABSTRACT

To verify the susceptibility of Spodoptera fugiperda, the most important pest of maize, to Bacillus thuringiensis (Bt), this study was carried out with 58 isolates belonging to W. H. O. Collaborating Centres for Entomopathogenic Bacillus of Institut Pasteur, Paris. For each isolate, 20 larvae of second instar were used, being individualized in well-contained artificial diet and where 3 x 10⁷ cells of this entomopathogenic bacterium were applied in each well. The selected isolate was evaluated concerning its LC₅₀, with 6 concentrations and control, in three replications, totaling 1,050 insects. The mortality, in both cases, was followed during seven days after treatment. Bt morrisoni isolate was the most pathogenic with 80% of mortality. Other 7 isolates caused mortality between 40 and 15%, 3 isolates below 15%, and all remainders were not active to this pest. In the virulence assay Bt morrisoni showed an LC₅₀ of 8.6 x 10⁶ cells/mL.

KEY WORDS:
Biological control; entomopathogen; fall armyworm; integrated pest management.