Selection of native isolates of Beauveria bassiana (Ascomycetes: Clavicipitaceae) for the microbial control of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae).

Previously undiscovered isolates of Beauveria bassiana (Balsamo) Vuillemin (Ascomycetes: Clavicipitaceae) able to control Rhipicephalus (Boophilus) microplus (Canestrini) (Acari: Ixodidae) were obtained for the first time in Argentina. The isolates were selected from three sources: 1) soil samples from the provinces of Corrientes, Formosa, and Chaco, where ticks are endemic; 2) dead female ticks; and 3) the fungal collection from the Entomopathogenic Fungi Laboratory of IMYZA-INTA Castelar. To select the isolates, population parameters were estimated, LC50 values of the most virulent isolates were calculated, and fungi-acaricides compatibility assays carried out. Isolates B. bassiana 259 and 98 were the most virulent and effective to reduce the number of eggs, the percentage of larval hatching, and parameters rm (natural intrinsic growth rate) and lambda (infinite growth rate) of Rh. (Bo.) microplus populations. The values of LC50 were 1 x 10(7) and 1.15 x 10(7), respectively, when applied to Rh. (Bo.) microplus eggs. In addition, they were compatible with acaricides. A novel methodology to evaluate the entomopathogenic activity of fungi on Rh. (Bo.) microplus ticks is introduced.