Effectiveness of granular formulations of Metarhizium anisopliae and Metarhizium brunneum (Hypocreales: Clavicipitaceae) on off-host larvae of Dermacentor albipictus (Acari: Ixodidae)

There is a critical need to develop effective, high-quality, fungal-based biopesticides for use against ticks. Dermacentor albipictus, the winter tick, is a one-host species that can cause mortality in large ungulates, particularly moose (Alces alces). The larval stage of this species aggregates on the ground in a prolonged, quiescent state during the summer and then quests for hosts in autumn. This behaviour offers an opportunity to treat a vulnerable life stage with entomopathogenic fungi in an environment where both are acclimated. We produced granular formulations of Metarhizium brunneum (Petch) and Metarhizium anisopliae (Metschn.) Sorokin, and tested their efficacy against winter tick larvae under semi-natural conditions within the laboratory. When granules were applied at rates of 5.0 × 10⁵ and 1.5 × 10⁷ conidia/cm², mortality ranged from 53–91% and 58–98% after nine weeks, respectively. Overall, the granular formulations had a similar ability to cause mortality to winter tick larvae regardless of application rate. Fungal granules persisted for nine weeks post application at concentrations of 9 × 10⁴–6 × 10⁵ CFU/g. These results demonstrate the potential of granular formulations of Metarhizium to persist and kill a one-host tick whose larvae have a prolonged off-host stage.