The hydro-chemical and physical conditions of the environment of the immature stages of some species of the simulium (Edwardsellum) damnosum complex (Diptera).

Water samples were collected from breeding sites of species of the Simulium (Edwardsellum) damnoslm complex in Upper Volta, Liberia and Cameroon during the dry season; and in Tanzania and Kenya at various seasons during a period of two years. The following 20 factors were analysed at 45 breeding sites: water temperature, current velocity, pH value, conductivity free carbon dioxide, oxygen content, calcium, magnesium, potassium, sodium, alkalinity, chloride, sulphate, nitrite, nitrate, ammonium, phosphate, silicate, total iron and organic substance (consumption of potassium permanganate). A number of notable differences in the chemical composition of the water of the breeding sites of 13 S. damnosum complex species were found, particularly with regard to the pH and conductivity. On the basis of these differences the various species can be divided into three main groups: Group I: 3 species (S. sanctipauli, S. yahense, "Menge"); breeding in sites with pH values always below 7 and conductivity values below 50 mumhos. Group II: 8 species (S. sirbanum, S. sudanense, S. damnosum s.s., S. squamosum, "Sanje", "Nkusi", "Nyamagasani", "Jovi"); breeding in watercourses with neutral, weakly acid or weakly alkaline reactions and conductivity values ranging from 50 to 150 mumhos. Group III: 2 species ("Kibwezi", "Kisiwani"); breeding in watercourses characterized by highly alkaline reactions with pH values between 7.7 and 10 and by conductivity values between 400 and 950 mumhos. The vectors of Onchocerca volvulus are included in group I and II only.