Biting behaviour and potential vector status of anthropophilic blackflies in a new focus of human onchocerciasis at Minacu, central Brazil

Monthly collections were made of man-biting female blackflies: Simulium aur ipellitum Enderlein, S. guianense Wise, S. minusculum Lutz and S. nigrimanm m Macquart (Diptera: Simuliidae) from four catching stations in the newly d iscovered focus of human onchocerciasis at Minacu (13 degrees 35'S 48 degre es 18'W), 300 km north of Brasalia in Goias State. These provided baseline data on biting habits, population density and seasonal prevalence during th e year before completion of the Serra da Mesa hydroelectric dam on the Rio Tocantins near Minacu, in a project investigating the effect of dam constru ction on onchocerciasis transmission in the area. All four simuliid species were most abundant during the dry season, and only bit in low numbers (S. auripellitum S. minusculum, S. nigrimanum) or were absent (S. guianense) in the wet season. Simulium minusculum was the predominant species at all cat ching stations, being particularly abundant by the large River Tocantins. T he other three species were mainly associated with smaller rivers. In the d ry season, biting rhythms of S, minusculum varied with catching site, while S. nigrimanum showed peaks of activity in early morning and during the aft ernoon. Experimental infection with Onchocerca volvulus (Leuckart) (Nematod a: Onchocercidae), from a human volunteer, showed that this parasite could develop fully in the four simuliid species, which are all considered to be potential vectors in the area.