ABSTRACT The characterization of selected Bacillus thuringiensis strains isolated from different Latin America countries is presented. Characterization was based on their insecticidal activity against Aedes aegypti , Culex quinquefasciatus , and Anopheles albimanus larvae, scanning electron microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and plasmid profiles as well as PCR analysis using novel general and specific primers for cry and cyt genes encoding proteins active against mosquitoes ( cyt1 , cyt2 , cry2 , cry4A , cry4B , cry10 , cry11 , cry17 , cry19 , cry24 , cry25 , cry27 , cry29 , cry30 , cry32 , cry39 , and cry40 ). Strains LBIT315, LBIT348, and IB604 showed threefold higher mosquitocidal activity against A . aegypti and C . quinquefasciatus larvae than B . thuringiensis subsp. israelensis and displayed high similarities with the B . thuringiensis subsp. israelensis used in this study with regard to protein and plasmid profiles and the presence of cry genes. Strain 147-8906 has activity against A . aegypti similar to that of B . thuringiensis subsp. israelensis but has different protein and plasmid profiles. This strain, harboring cry11 , cry30 , cyt1 , and cyt2 genes, could be relevant for future resistance management interventions. Finally, the PCR screening strategy presented here led us to identify a putative novel cry11B gene.