Laboratory Bioassays of a Native Arkansas Isolate of Metarhizium robertsii (Hypocreales: Clavicipitaceae) for the Control of Amblyomma americanum (Acarina: Ixodidae)

Abstract

Incidences of tick bites and associated diseases have increased perhaps due to human encroachment into habitats harboring higher densities of ticks and mammalian hosts (Trout 2010, Raghavan et al. 2019). The lone star tick, Amblyomma americanum L. (Acarina: Ixodidae), an American species, comprises ∼75% of ticks collected from people, wildlife, and vegetation in Arkansas (Loftin & Smith 2019). In addition to being a nuisance, this tick’s bite can transmit harmful human and animal pathogens, e.g., ehrlichiosis, tularemia, bobcat fever, and some spotted fever rickettsioses, and can cause alpha-gal syndrome, an acute debilitating allergy to red meat (Nicholson et al. 2018). Where ticks become problematic, chemical acaricides are often sprayed onto vegetation or topically applied to animal hosts (Ostfeld et al. 2006). Although these acaricides are relatively safe when used properly, their area-wide use may result in the contamination of soil, water (Kunz & Kemp 1994), milk and meat (Falowo & Akimoladun 2019), as well as lead to acaricidal resistance (Abbas et al. 2014). In response, a search for alternative acaricidal agents has been well underway (White & Gaff 2018). Entomopathogenic fungimay be useful as a self-propagating, area-widemethod of tick control with active ingredients (i.e., infectious spores) being derived from the soil or from infected hosts themselves (Tuininga et al. 2009). These asexual spores or conidia penetrate the tick exoskeleton or egg chorion, thereby infecting all growth stages: eggs, nymphs, larvae, and adults (Samish et al. 2008). The most studied virulent entomopathogens for tick control include strains of Beauveria species (Hypocreales: Cordycipitaceae) andMetarhizium species (Hypocreales: Clavicipitaceae). Pathogenicity of Metarhizium strains against A. americanum is receiving more attention (Gomathinayagam et al. 2002, Kirkland et al. 2004,