Control of Boophilus microplus larvae by Metarhizium anisopliae in artificially infested pastures

The objective of this work was to evaluate the efficiency of Metarhizium anisopliae fungus against Boophilus microplus population in Brachiaria brizantha and Tifton 85 (Cynodon) pastures, artificially infested with tick engorged females. Thirty plots of I m(2) each were randomly distributed in fifteen treated and fifteen control groups per type of grass, establishing five repetitions for each treatment. Pastures were infested with engorged tick females standardized by number and weight. Metarhizium anisopliae suspension with 1.8x10(8) conidia mL(-1) concentration was sprayed on the plot in three different assays, prior infested with tick females, immediately after tick inoculation and at first larvae emergency. The fungus action was evaluated at 35(th), 38(th), 41(st), 48(th), 55(th) and 61(st) day post infestation by counting recovered larvae. A significative reduction of larvae counts occur-red in fungus treated groups during 35(th) to 48(th) day post infestation, ranging between 87% and 94% of efficacy on tick larvae control. The mean values for larvae counting in Tifton 85 pasture were lower than in B. brizantha plot in all analysis, suggesting the pasture effect on fungus action. Treatment strategy influenced on M. anisopliae activity, which demonstrated better results at 41(st) and 55(th) day post infestation in B. brizantha, submitted to conidia challenge after larvae emergency.