| Trichomycetes are a cosmopolitan group of symbionts in arthropods and are common in aquatic larvae of the Diptera. The organisms grouped under the name trichomycetes belong to two major taxa. One taxon contains three fungal orders in the class Trichomycetes (Zygomycota) and the other taxon contains one nonfungal order (Amoebidiales). Most previous studies have addressed taxonomic aspects and physiology of the relatively few cultured species. The main objective of this study was to investigate colonization of black flies (Diptera: Simuliidae) by trichomycetes. Aspects of colonization treated are temporal changes in prevalence, prevalence related to stream ecological conditions, structural/physiological aspects of colonization, colonization by rare species, and formation of sexual spores (zygospores) in trichomycetes. Study sites were in Oconee and Pickens Counties, South Carolina, USA. Ten species of trichomycetes were found, including Harpella melusinae, Paramoebidium chattoni, Paramoebidium curvum, Genistellospora homothallica, Pennella nr. hovassi, Simuliomyces microsporus, Smittium coloradense, Smittium culisetae, Smittium megazygosporum, and Stachylina pedifer.; Harpella melusinae, Paramoebidium chattoni, and Simuliomyces microsporus had seasonal differences in prevalence in one stream. Prevalence of Harpella melusinae was nearly 100% except in winter. Paramoebidium chattoni and S. microsporus had lower prevalences in summer.; A principal components analysis was used to examine the relationship between prevalence of Harpella melusinae and stream conditions (e.g., dissolved oxygen, pH, velocity). A relationship between pH and conductivity for Simulium tuberosum and velocity for S. verecundum was found.; A rare species of trichomycete (Smittium megazygosporum) was found. The large zygospores of this species might enable it to exist in a resting state for long periods. Host-dependent variation in the size of the asexual trichospores was also demonstrated.; Zygospores of the midgut-inhabiting Trichomycetes have been rare in previous studies. High pH and potassium were used to induce zygospore formation when field-collected conjugating thalli (less rare than zygospores) were available. The first zygospores of a typical species of Stachylina ( S. pedifer) were induced. The zygospores are morphologically similar to the zygospores of Harpella melusinae, another midgut-inhabiting trichomycete. The first zygospores of the hindgut-inhabiting Smittium coloradense were discovered in chironomid midges. |
