Abstract

Bacillus thuringiensis (Bt) endotoxins (Cyt and Cry) have been extensively explored for biological control of fall armyworm, Spodoptera frugiperda, an important pest in major corn-producing countries of America. Five hundred Bt isolates with different toxicities against S. frugiperda were characterized by PCR for the presence of cyt genes (cyt1, cyt2, cyt1Aa, cyt1Ab, cyt2B and cyt2Ba), and the effect of insecticidal proteins Cry1Ba, Cry1Ca, Cry1Da and Cyt on S. frugiperda larvae were evaluated. Six isolates showed the presence of cyt genes, three isolates harbored two gene families (cyt1 and cyt2), and three isolates harbored only one of the cyt gene families (cyt1 and cyt2). It was not possible to correlate the presence/absence of cyt genes with toxicity against S. frugiperda. In this study, cyt genes were present in toxic and nontoxic isolates to this insect pest. Bioassays against S. frugiperda larvae showed that only Cry1Ca protein had toxicity, with 77.08% of mortality. Synergism among Cry and Cry proteins used in this study against S. frugiperda was not observed.

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