Trichomycetes: Fungi in Relationship with Insects and Other Arthropods

Concluding remarks

Trichomycetes are unique among symbiotic fungi. Their adaptation to living in arthropod guts has resulted in many structural and functional features that make them distinct from other Zygomycota. A worldwide distribution of Trichomycetes and the wide range of arthropod types and habitats to which they have adapted are evidence of their evolutionary success.

Parasitism that results in death of the host currently is know only in one species, Smittium morbosum, in mosquito larvae. However, several Harpellales in blackfly larvae have been found at particular times of the year to invade the ovaries, which become filled with fungal cysts that are “oviposited” by the sterile female. It is postulated that this mechanism of fungal dispersal by adults may have evolved in all species of Harpellales, given that they normally inhabit only larval stages.

Trichomycetes share arthropod guts with a range of prokaryotes, nematodes, and protozoans. In those symbiotic relationships where effects on the host are subtle, it is necessary to distinguish between the consequences of fungal activity and that of other microorganisms in the gut if the role of the mycobiont is to be experimentally ascertained. A study by Horn (1980) using axenically raised larvae of Aedes aegypti and a culture of Smittium culisetae showed that the gut fungus could provide a benefit by supplying some of the required sterol and B-vitamins when the mosquito larvae were deprived of those essential nutrients. Thus, in Trichomycetes that normally appear to be commensalistic, their symbiotic roles may not be obvious, or may change, depending upon the species and circumstances.