Enhanced activity of Beauveria bassiana to red imported fire ant workers (Hymenoptera : Formicidae) infected with Thelohania solenopsae

R range of concentrations of Beauveria bassiana (Balsamo) Vuillemin conidia was tested against red imported fire ant, Solenopsis invicta Buren, worker s from colonies infected with the microsporidian, Thelohania solenopsae Kne ll, Alien, and Hazard, and on workers from healthy colonies. Median lethal concentrations (LC50) of B. bassiana in healthy and microsporidian-infected colonies showed that fire ants from infected colonies were more susceptibl e to B. bassiana infection than ants from healthy colonies. The LC50 of B. bassiana in microsporidian-infected workers was 4.5X less than that of heal thy colonies. Mortality of ante from T, solenopsae-infected colonies that w ere treated with 9.66 x 10(6) B. bassiana colony forming units per cm(2) wa s subadditive compared to either pathogen alone.