Inability of the lone star tick, Amblyomma americanum (L.), to resist desiccation and maintain water balance following application of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae (Deuteromycota)

We report that female lone star ticks (Amblyomma americanum) experience a rapid change in water permeability when treated with the entomopathogenic fungus Metarhizium anisopliae. The amount of water loss is nearly double the rate of control ticks not exposed to this fungus. As a result, ticks are prevented from stabilizing body water levels (water gain * water loss) at hydrating atmospheres greater than the critical equilibrium activity (CEA) of 0.85a _v-0.93a_v (a_v = % RH/100) and reach their dehydration tolerance limit in less time. Thus, disruption of water balance is a pathogenic consequence of fungus infection. This served as a benchmark for evaluating effects on ticks of frequently encountered soil molds in nature (wild tick isolates), Aspergillus niger, Cladosporium cladosporioides, Penicillium glabrum and Scopulariopsis brevicaulis. In contrast to M. anisopliae treatment, no effect on tick water balance was noted with topical application of C. cladosporioides, but water loss rates of ticks following treatment with S. brevicaulis fell between both extremes. Water loss rates imply that P. glabrum may be a tick pathogen, whereas A. niger is apparently not able to use ticks as a substrate. Enhanced desiccation arising from these common molds shows the importance of local mycoflora as natural regulators of tick populations. Water loss rates also provide a tool to assess the pathogenicity of different fungal strains targeted for application in the biological control of ticks.