Isolation of Bacillus strain toxic to Spodoptera frugiperda (Lep.: Noctuidae)

Abstract

Introduction. The fall armyworm, Spodoptera frugiperda (Sf), is one of the most important corn pests in tropical and subtropical America. Some microorganisms are important candidates for its control. Bacillus thuringiensis (Bt) is an entomopathogenic sporeforming bacterium, which produces proteinaceous crystalline parasporal inclusions (Cry). Objective. Evaluation of ten “Cry” producer strains against first instar larvae of Sf. Materials and methods. Individuals comes from a laboratory colony maintained under controlled conditions (25°C, 70-75% RH and 12:12 L/D). The artificial diet was immersed in sterile water “Cry” protein suspension. Microorganisms isolated from soil and dead larvae were used. Larval mortality was determined during 7 days. Results and conclusions. One of the native strains tested, called RT3, had a strong toxicity against Sf larvae. Considering two independent assays, a mortality level from 76.6 (F=60.50; gl=1; P=0.0015) to 100% was observed after 3 and 4 days, respectively. Finally, in the first assay no larva was survived. Larval mortality using serial dilution of “Cry” suspension was also determined. According to these results, the isolated RT3 can be considered an active strain. This work were supported by grant CIUNT D308 and CONICET