An emulsifiable concentrate (EC) and granular (G) formulation of the entomopathogenic fungus, Metarhizium brunneum strain F52 (formerly Metarhizium anisopliae strain F52) were tested against unfed adults and nymphs of Ixodes scapularis Say in the laboratory. Three exposure methods; dip, surface contact, and direct spray application, and three exposure time intervals (3, 30, and 300 min) were used to evaluate the EC formulation. Application rates ranged from 2.6 × 102 to 2.6 × 108 conidia/cm2. The surface treatment was used for granular formulation with concentrations ranging from 2.3 × 105 to 2.3 × 107 conidia/cm2 for same three exposure times. Both the EC and G formulations of this fungus were highly pathogenic against I. scapularis adults and nymphs. Logistic regression analysis found formulation, spore concentration, time of exposure, and observation period were significant or highly significant factors influencing tick mortality. For adult I. scapularis, the spray application with the EC formulation of M. brunneum F52 resulted in a lower LC50 (5.9 × 104 conidia/cm2) at 30 min than surface exposure to the EC (LC50 = 1.3 × 106 conidia/cm2) or G formulation (LC50 = 8.1 × 105 conidia/cm2). At higher concentrations, fungal activity was evident in adult I. scapularis held at 5°C suggesting the fungus may provide control in the cooler fall season. While the observed pathogenicity of a fungus against ticks can be dependent upon the bioassay assessment, we found nymphs and adults of I. scapularis to be highly susceptible to M. brunneum F52, regardless of the exposure method used.
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