Virulence of Brazilian selected strains of Beauveria bassiana (Balsamo) Vuillemin, their infectivity at different temperatures and horizontal transmission potential on adults of Cosmopolites sordidus (Germar) (Coleoptera Curculionidae) were investigated. No relation was observed between groups formed by molecular analysis and the biological activity of tested B. bassiana against C. sordidus in preliminary screening bioassay. LC50 after a ten-day period was 3.9 x 10(7) and 2.6 x 10(8) conidia ml(-1) for the selected strains CG1013 and CG1027, respectively. LT50 at 21, 25 and 29 degrees C was less than 7.4 days for a 2 x 10(8) conidia ml(-1) suspension of CG1013. LT50 for CC 1027 were up to 11 days for the same temperatures. Fungal transmission occurred among infected and healthy individuals. Density increase of inoculated insects in the population increased the mortality of non-inoculated insects for both strains. The number of conidia produced per cadaver was similar for the two strains. However, horizontal transmission efficacy of CG1013 was higher than that observed for CG1027. Mortality of non-inoculated adults at a ratio of 2:10 of infected to healthy adults was 10% for CG1027, after 20 days of exposure. At the same ratio, mortality of non-inoculated insects was 34% for CG1013. Our results indicate the potential of the strain CG1013 of B. bassiana as a biocontrol agent against the banana weevil.