Online

Sullivan, Cheryl Frank

Plant and Soil Science

2021

Ph. D.

There is a critical need to develop effective, high-quality, fungal-based biopesticides for use against ticks. Dermacentor albipictus Petch (Acari: Ixodidae), the winter tick, is a one-host tick. They commonly infest large ungulates, particularly moose, Alces alces L. (Artiodactyla: Cervidae) on which they cause significant physiological and metabolic stress on densely parasitized individuals. Heavily infested calves can be killed. Entomopathogenic fungi in the genera Metarhizium (Hypocreales: Clavicipitaceae) and Beauveria (Hypocreales: Cordycipitaceae) are promising tick biological control agents. The larval stage of D. albipictus aggregates on the ground in a prolonged, quiescent state during the summer and then quests for hosts in autumn. This behavior offers an opportunity to treat a vulnerable life stage with entomopathogenic fungi in an environment where both are acclimated. The objective of this research was to evaluate the efficacy of commercial fungus-based biopesticide products and test new fungal isolates and formulations containing M. anisopliae, M. brunneum and B. bassiana against the larval stage of D. albipictus in vitro and under semi-natural conditions in the laboratory. This was conducted to determine the potential of these fungal pathogens for use within an integrated tick management program in areas where ungulates may recruit large numbers of ticks. Results showed D. albipictus larvae were susceptible to experimental and commercially formulated isolates of M. anisopliae, M. brunneum and B. bassiana to varying degrees depending on formulation type, application rate and treatment timing during their off-host life stage. In general, Metarhizium caused significantly greater mortality than Beauveria when applied at the same rate and spray applications were more efficacious in a shorter amount of time than granular applications. This research provided new information on the effectiveness of different formulations of B. bassiana, M. anisopliae and M. brunneum and different application methods against D. albipictus larvae. In particular, the potential for Metarhizium granular formulations to persist and kill a one-host tick species whose larvae have a prolonged off-host stage, free-living in the environment was demonstrated. Field trials should be attempted to advance the use of fungal-based biopesticides against ticks.