Summary: Black flies (Diptera, Simuliidae) and their role as disease vectors with respect to changing environmental conditions
Black flies (Diptera, Simuliidae) have a worldwide distribution. Their developmental stages inhabit all kinds of lotic waterways. The sessile larvae are filter feeders, which often form a large proportion of the benthic biomass.
Against the value of the immature stages in the food chain must be set the harm caused to man and other vertebrates by the adult black flies. Simuliids can impact vertebrates in a variety of ways and for this reason are of considerable economic importance. Black fly females of many species are serious biting pests in many regions on all the continents simply because they feed on blood.
Under certain environmental conditions some show mass development, particularly along large lowland rivers. As a result, the haematophagous females attack potential blood hosts in huge numbers and cause serious pest and nuisance situations. Cases of simuliotoxicosis in cattle and simuliosis in humans may follow.
Furthermore, black flies are obligate vectors of disease agents affecting humans, livestock and poultry in certain regions of the world: Dirofilaria, Mansonella, Onchocerca (Kinetoplastida: Onchocercidae) and Leucocytozoon (Apicomplexa: Plasmodiidae). A role of saliva components of the simuliids as co-factors supporting the transmission of human herpes-viruses is discussed.
For onchocerciasis control in Africa, larvae of the genus Simulium are periodically treated with chemical and/or bacterial larvicides. Simuliid control by biocides is mainly based on “biological” products such as Bacillus thuringiensis var. israelensis (Bti) toxin.
Changes in the ecosystem, such as structural alterations of the river landscape, changes in water quality or changes in river management, may directly or indirectly affect the developmental conditions of simuliid black flies in a positive or negative sense.