Vertical transmission of the entomopathogenic soil fungus as a contaminant of eggs in the winter tick, , collected from calf moose (New Hampshire, USA).

Moose naturally acquire soil fungi on their fur that are entomopathogenic to the winter tick, . 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 () were used to investigate the presence and extent of fungal infection. Approximately 40% of eggs and larvae were infected, almost exclusively by the fungus (teleomorph : Microascaceae, Ascomycota). Eggs analysed on the day of oviposition and day of hatching had high frequency (40%) of , whereas the frequency in eggs harvested was minimal (7%); therefore, exposure occurs pre-oviposition in the female's genital chamber, not by transovarial transmission. At hatching, larvae emerge containing indicating transstadial transmission. Artificial infection by topical application of eggs and larvae with a large inoculum of 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 is maintained as a natural pathobiont in winter ticks.