Effects of some Hydrophysico-Chemical Factors on the Distribution of Simuliids in Kaduna State, Nigeria
MBAH, C.E. and NOCK, I.H.
ABSTRACT: A survey of Simulium breeding sites was undertaken in Kaduna State between September 1990 and July 1995. Immature and adult simuliids were collected from rivers and streams across four bioclimatic zones (the Sudan Savanna, Montane Savanna, Northern Guinea Savanna and Southern Guinea Savanna) comprising 65 stations in 20 sites. It was designed to obtain pre-control baseline data for the control of onchocerciasis in the Kaduna endemic foci and adjacent areas. The breeding site distribution of simuliid fauna is, to a large extent, influenced by the bioc1imatic zonation and hydro-physicochemical
characteristics of a particular area. Variation of water current velocity with the rivers and between the rivers and months were also highly significant (P < 0.01). The three anthropophilic species namely Simulium damnosum s.s, S. sirbanum and S. squamosum were the most abundant at very high velocities (2.0-2.6 m!s), and at higher temperatures (24-28.8 DC), and preferred a pH
range of 6.0-7.8. The immature stages of non anthropophilic black flies such as S. hargreavesi and S adersi occurred in both moderate (1.0-1.9 m/s) and
higher (2.0-2.5 m!s) water velocities with a temperature range of 20-27 °c and pH 6.0-7.2. Simulium ruficorne and S. alcocki preferred sluggish, slow water velocities (0.1-1.4 m/s), temperatures 21.5-27 °c and pH range 6.0-7.2. Slight variations in one or more of the hydrochemical parameters within the breeding sites enabled simuliids breed communally and could limit the occurrence of each species in the microniche.