Multiple symbiotes in larval black flies (Diptera: Simuliidae): associations of trichomycete fungi with ichthyosporeans, mermithid nematodes, and microsporidia

Studies of the interactions between two or more species of symbiotic microorganisms in a single host animal have lagged behind those involving interactions between hymenopteran or dipteran parasitoids. We screened the larvae of four species of black flies (Cnephia ornithophilia, Simulium furculatum, Simulium innoxium, and Simulium vandalicum) to determine if the colonization and prevalence of trichomycete fungi were influenced by ichthyosporeans, mermithid nematodes, microsporidia, or other species of trichomycetes. Differences in the layering of the peritrophic matrix of microsporidian-infected larvae, compared with that of uninfected larvae, were associated with greater levels of colonization by the midgut-inhabiting trichomycete Harpella melusinae. Colonization levels of different species of trichomycetes were significantly correlated with one another in only 2 of 11 cases. Aside from the consistent attachment of the trichomycete Simuliomyces microsporus to the ichthyosporean Paramoebidium chattoni, we found little evidence that prevalence and colonization levels of trichomycetes were influenced by other symbiotes, including other trichomycetes. This trend might reflect the physical separation of trichomycetes, which are gut specific, from other symbiotes. In addition, any combinations of symbiotes that were wholly incompatible would not have been observed in our field-collected material.