Myrmicinosporidium durum, an Enigmatic Fungal Parasite of Ants

Abstract

Myrmicinosporidium durum is an uncommon parasite of ants with unclear affinities. We present evidence of the fungal nature of this organism. The ants Pogonomyrmex barbatus, Chalepoxenus muellerianus (Myrmicinae), Plagiolepis vindobonensis , and Plagiolepis pygmaea (Formicinae) are new hosts reported for M. durum. The presence of this parasite is also reported for the first time from the Western hemisphere (host, P. barbatus, Texas). A list of the known hosts and localities is given. M. durum infection is nearly parasitic, chronic, and the fungus sporulates heavily in the living host's hemocoel; infected ants are long-lived, darker in color, and display normal behavior. Spores (sporangia?) are dark brown, >35 μm in diameter. The spores are multinucleate; nuclei are indistinct and small (2 μm in diameter). The vegetative phase of M. durum (parasitizing the ant Leptothorax unifasciatus from Italy) is described here for the first time. Its development in the hemocoel of insects, the thin-walled myceliar thallus, the endogenous production of spores in the swollen hyphal tips, and a possible dehiscence line in the spores indicate a relationship with Coelomomyces in the Chytridiomycetes. Analogies to other entomopathogenic fungi (especially Entomophthorales) are discussed.