Hydro-Physicochemical Changes in Domasi River Associated with Outbreak of Blackflies (Diptera; Simuliidae) in Zomba, Malawi

Abstract

Blackflies impact human and animal health due to their biting nuisance and transmission of Ochocerca volvulus. This study presents an attempt to analyze hydro physicochemical changes associated with outbreak of black flies in Zomba, Malawi. The study compared historical data of hydro physicochemical parameters before (1985-2002) and after (2008) the outbreak to deduce the changes associated with mass occurrence of these flies. Changes in water quality between these two periods were assessed using T-tests. To establish the relationship between the black fly larval densities and water quality parameters data was subjected to both principal component and correlation analysis. Three principal components before the outbreak and two principal components during the outbreak (both dry and wet season) accounted for most of the variation in water quality in this river system. Nutrient load, increases in Total Suspended Solids (TSS) and Total Hardness (TH) were the main factors that had high loadings on these principal components over the years. A significant correlation was established between black fly larval densities and total hardness (r=0.86, p<0.05) as well as total suspended solids (r = 0.755, p<0.02). The potential role of anthropogenic influences on water quality and its cascading effect on black fly population dynamics is discussed.