The Tripartite Relationship between Mushrooms, Mycetophilid Gnats, and Nematodes

Abstract

The genus Iotonchium is one of the nematode groups utilizing fruiting bodies of basidiomycetous fungi. They have two ecological phases in their life cycles, i.e., mycetophagous phase living in mushrooms and insect-parasitic phase parasitizing mycetophilid gnats. In this genus, 11 species have been reported in the world, however, only 5 species, including 4 Japanese species, have been clarified the details of their life cycles. Iotonchium ungulatum, a pathogen of gill-knot disease of the oyster mushroom, is known to generate nematode-galls (knots) on the gills of fruiting bodies of Pleurotus fungi. Other Iotonchium species do not generate knots and inhabit the tissue of fruiting bodies of host fungi. Iotonchium nematodes are supposed to have close relationships with mycetophilid gnats. In the amber, their relative species has been discovered with the mycetophilid fossil. This review highlights the tripartite relationship of these organisms and discusses their evolutionary relationship and the future directions of research on this topic.