Abstract

Blackflies are one of the insects of medical importance because of the parasites they transmit and the biting nuisance they cause. These flies have aquatic larvae and pupae that require fast flowing water for their development. Changes in the environment can make the blackflies reach pest proportions and cause outbreak. A study on the potential ecological changes associated with the outbreak of the blackflies was carried out. Changes in the physicochemical parameters of the water in Domasi river in one of the affected areas were analyzed. The test parameters included; total suspended solids, total hardness, total alkalinity, temperature, pH, electrical conductivity, dissolved oxygen, nitrates and phosphates. Recent water physicochemical data (2008) was collected and compared with historical physicochemical data (1985-2002) of the river to investigate the changes in the concentration in the parameters over the years. The data was later analyzed for the principle components (PC) that controlled the water quality for Domasi river over the years. The test parameters were reduced to 2 factors in September (2008), December (2008), and 3 previous years by principal component analysis (PCA). The spatial variation of the test physicochemical constituents was then plotted. The results of the factor scores were represented as contour diagrams to deduce their spatial variation. The data of the test parameters (for previous years and present) was further analyzed for significant changes over the years using students’t-test. The test parameters that showed a significant change (p<0.05) over the years were tested for associations with blackfly larval densities. Larval densities positively correlated with total hardness (r=0.859, p<0.05) and total suspended solids (r = 0.755, p<0.02). Furthermore, we examined changes in forest cover in the affected area. Land sat images of the years; 1984, 1994 and 2004 were used. The images were processed using Ilwis software and Arc GIS 9.2 was used to map the cover change. Results indicated that there has been significant ecological changes mainly in the concentrations plus spatial variation of the physicochemical constituents and forest cover in the affected area. It was evident that the outbreak of the blackflies in Zomba may have been mainly due to increases in total hardness and total suspended solids. The changes in the forest cover contributed to the changes in the water quality and the alteration of the microclimates in the sites where blackflies rest and breed, shortened their gonotrophic cycles and led to population outbreak.

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School	: School of Natural and Applied Sciences
Issued Date	: 2010

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