Characteristics of managed and unmanaged water bodies influencing their suitability as mosquito breeding habitats in Bahir Dar, Ethiopia

Abstract: Mosquito-borne diseases like malaria, dengue fever, yellow fever and West Nile virus are serious problems in many parts of the world, especially in Africa, and partially in Ethiopia. Millions of people become infected and several hundred thousand people die worldwide from these diseases every year. The most conventional methods for mosquito vector control target female adult mosquitoes in a reactive way using insecticides. However, it is possible to perform proactive vector control through source reduction. The main focus of this study was to investigate if there are any associations between characteristics of managed still water bodies and the presence of mosquito larvae in Bahir Dar, Ethiopia. This was done by measuring twelve variables, both abiotic and biotic; pH, conductivity, dissolved oxygen, turbidity, biochemical oxygen demand, nitrate, phosphate, sulphate, carbonate, depth and presence of algae as well as collecting and counting mosquito larvae in ten different sites, during a time series of five weeks. The most common managed waters believed to serve as efficient breeding habitat for mosquitoes were ponds and ditches used for irrigation, drainage or cultivation. A total of 204 mosquito larvae were collected, where 95% were found in four of the ten sites, three of them were managed waters and the last one was unmanaged. Statistical analyses were performed in order to examine potential correlations and differences among the sites. Wilcoxon test was performed to investigate differences between managed and unmanaged waters. Simple linear regression analyses were performed to identify driving variables for the presence of mosquito larvae. The main results from the group tests were significant differences in mosquito larvae density between managed and unmanaged sites. Significant differences between mosquito sites and zero-sites for dissolved oxygen and sulphate were found. Simple linear regression revealed pH and dissolved oxygen as driving variables for mosquito larvae presence. It was concluded that resources should be put on treatment or manipulation of ponds, which were considered the preferred mosquito breeding habitats. However, if conflicts arise among interests concerning food production, measures must be planned and performed thoughtfully or focus should be put on less controversial breeding habitats. Among the driving variables, dissolved oxygen was the suggested variable to manipulate in order to reduce mosquito larvae populations.