Chironomidae-Trichomycete associations: a literature review.

Published records of Chironomidae serving as hosts for Trichomycete fungi are summarized and citations to original literature provided. Fifty-one species of Tricho mycetes from the order Harpellales are reported to occur in 32 genera within the subfamilies Orthocladiinae (12 genera), Chironominae (10), Diamesinae (7), and Tanypodinae (3). Thirty of the Trichomycete species are known only from hosts within a single subfamily or tribe, and no species occur in hosts from all four subfamilies. Orthocladiinae serve as hosts for 29 Trichomycete species, Chironominae hosts 21 species, Diamesinae 13 species, Tanytarsini 11 species, Tanypodinae 4 species, and Pseudochironomini hosts one Trichomycetes species. Or thocladiinae also has the greatest number of Trichomycete species that occur only in spe cies of this subfamily with 14. Chironomini and Tanytarsini show the greatest overlap in Trichomycete infestations, followed by Diamesinae and Orthocladiinae. Fifteen additional species of Trichomycetes are recorded in the literature from chironomids but no host genera are listed, bringing the total to 66 species of Trichomycetes associated with Chironomidae. The fungal genus Smittium has the greatest number of species associated with Chironomidae hosts, with 43 Smittium species infesting chironomid larvae compared to Stachylina (16), Aus trosmittium (4), Furculomyces (2) and Trichozygospora (I). Twenty three new, but incom plete, records included in this publication are not included in the totals given above. Fungi of the class Trichomycetes (Zygomycota) live obligately within the diges tive tracts of arthropod hosts (Lichtwardt, 1986). Species of the order Harpellales at tach to the hindgut cuticle or peritrophic membrane of the midgut of immature aquatic Diptera, Ephemeroptera, Plecoptera, Trichoptera and Coleoptera. They are believed to associate with their hosts primarily as commensals, neither harming nor benefitting the hosts. However, at least one species, Smittium morbosum, can cause devastating mortality in larval mosquito populations (Sweeney, 1981; Sato et al., 1989), but other studies have provided evidence that gut fungi can benefit develop ing larvae that are nutritionally deprived (Horn and Lichtwardt, 1981). Five genera of Trichomycetes are associated with Chironomidae hosts. Two of the genera, Smittium and Stachylina, are cosmopolitan, and comprise 56% of de scribed Harpellales. Species of Stachylina are restricted to the peritrophic mem brane of the midgut as an attachment site. Species of Smittium all generally attach to only the hindgut cuticle, where growth and sporulation occur, although there is a recent report of premature sporulation and limited thallic growth in the midgut (Lichtwardt et al., 1997). The remaining three genera, Austrosmittium, Furcu lomyces and Trichozygospora, all attach to the hindgut. These genera are not spe cies rich, with Austro smittium only found in Orthocladiinae larvae from Australia and New Zealand, Furculomyces in larvae collected from Australia and central United States, and the monotypic Trichozygospora in hosts from the eastern United States and Europe. 1 Kansas Biological Survey University of Kansas, Lawrence, KS 66045, USA. 2 Department of Entomology, University of Kansas, Lawrence, KS 66045, USA. 3 Department of Botany, University of Kansas, Lawrence, KS 66045 USA. Accepted 22 April 1998. This content downloaded from 207.46.13.28 on Wed, 31 Aug 2016 04:18:01 UTC All use subject to http://about.jstor.org/terms VOLUME 71, ISSUE 4 491 Trichomycete associations are described for species in four of the Chironomidae subfamilies?Tanypodinae, Diamesinae, Orthocladiinae and Chironominae. Pub lished descriptions of Trichomycetes and Chironomidae hosts are scattered and no systematic appraisal has been made of the host/Trichomycete relationships. It ap pears that chironomid researchers are largely unaware of the extent to which larvae serve as hosts for the fungi, since they were not mentioned in sections dealing with host-parasite/commensal relations in Armitage et al. (1995). Consequently, the pur pose of this review is to compile a comprehensive list of the Chironomidae hosts, and to summarize patterns that exist among the fungi and their Chironomidae hosts. Methods and Materials Published Trichomycete and Chironomidae associations were compiled by a re view of the following literature: Lichtwardt, 1972, 1986, 1994, 1996, 1997; Licht wardt and Arenas, 1996; Lichtwardt and Grigg, 1998; Lichtwardt and Williams, 1983, 1988, 1990, 1992a, b, c; Lichtwardt et al., 1987, 1997; Manier, 1969; Williams and Lichtwardt, 1984, 1987, 1990, 1992. Unpublished Trichomycete and Chironomidae associations have been compiled from our previous and current studies, and include records from several chironomid hosts that could be identified to genus but usually with insufficient development of fungus to characterize it to species. Voucher spec imens of both fungi and chironomid hosts are kept in our respective labs at the Uni versity of Kansas and are available for inspection. Similarity of Trichomycetes infestations among Chironomidae subfamilies was measured using Whittaker's Coefficient of Percentage Similarity (Whittaker, 1952). This measure of similarity was chosen since Trichomycete infestations were con sidered to be meristic attributes, with the number of chironomid species of each sub family known to be infested by particular Trichomycetes used as input to calculate the index. However, no effort was made to determine the relative occurrence of in festation by a Trichomycete within a known host chironomid.