Speciation and Dispersal of Fungal Symbiots of Insects (Harpellales) in Eastern North America and Europe

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Abstract Harpellales, one of three orders of the class Trichomycetes, are fungi that live as symbionts in the guts of insects, particularly stoneflies (Plecoptera), mayflies (Ephemeroptera), and lower flies (Diptera: Nematocera). Typically, the fungus is transmitted from larval insect to larval insect, raising questions about how the fungi are dispersed over great geographic distances. Evidence exists that they may have a parasitic life stage in which cysts are formed in the ovaries of host insects that then disperse and deposit fungi in new habitats. Details of the association of these fungi with host insects are poorly known as are relationships among the fungi and explanations for their origins and diversification. Because host insects include many species of ecological and medical importance (e.g., mayflies and stoneflies, mosquitoes, black flies, biting midges), an understanding of parasitism that can result in sterilization of the host insect has great interest to entomologists. Field and laboratory studies will help unravel the interactions between these fungi and their hosts, including a molecular informed phylogeny for the fungi that can help explain their diversification and origins. This will permit a better understanding of a very enigmatic group of fungi, and make its species accessible to biologists interested in symbiosis, parasitism, historical biogeography, and possibly co-speciation.