Abstract
ABSTRACT Moose naturally acquire soil fungi on their fur that are entomopathogenic to the winter tick, Dermacentor albipictus. Presumed to provide a measure of on-host tick control, it is unknown whether these soil fungi impact subsequent off-host stages of the tick. Eggs and resultant larvae originating from engorged, adult female winter ticks collected from dead calf moose (Alces alces) were used to investigate the presence and extent of fungal infection. Approximately 40% of eggs and larvae were infected, almost exclusively by the fungus Scopulariopsis brevicaulis (teleomorph Microascus brevicaulis: Microascaceae, Ascomycota). Eggs analysed on the day of oviposition and day of hatching had high frequency (40%) of S. brevicaulis, whereas the frequency in eggs harvested in utero was minimal (7%); therefore, exposure occurs pre-oviposition in the female’s genital chamber, not by transovarial transmission. At hatching, larvae emerge containing S. brevicaulis indicating transstadial transmission. Artificial infection by topical application of eggs and larvae with a large inoculum of S. brevicaulis spores caused rapid dehydration, marked mortality; pathogenicity was confirmed by Koch’s postulates. The high hatching success (>90%) and multi-month survival of larvae imply that S. brevicaulis is maintained as a natural pathobiont in winter ticks.
Highlights
The utilisation of a single moose (Alces alces) by the winter tick Dermacentor albipictus, a one-host species, exposes winter ticks to numerous on-host fungi that are acquired by moose from soil in breeding wallows and bed sites
The purpose of this study was to determine the internal mycoflora of eggs and unfed larvae, with the goals of: (1) examining the extent that winter tick eggs and unfed larvae are infected with fungi as a residual of the adult female tick, (2) identifying fungi that infect winter tick eggs and larvae, whether a single, select fungus or mixture of fungal components are disease-causing, and (3) assessing the capacity for artificial infection by a topically applied large spore inoculum that serves to confirm pathogenicity to the egg and larval stages
Our study indicates that the mitosporic fungus S. brevicaulis is “inherited” in the wild from adult female D. albipictus
Summary
The utilisation of a single moose (Alces alces) by the winter tick Dermacentor albipictus, a one-host species, exposes winter ticks to numerous on-host fungi that are acquired by moose from soil in breeding wallows and bed sites. This exposure is presumed adaptive as a natural, bio-control of on-host tick abundance (Yoder et al 2018a, 2018b). These fungi are common soil saprobes and anamorphs of ascomycetes, that act as tick pathogens (entomopathogens) by producing copious amounts of spores as the primary transmission route of infection (Fernandes et al 2012). The hyphae have enveloped the tick within a mycelium that creates a mouldy “mummy”
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