Improvement of Water Quality for Mass Anopheline Rearing: Evaluation of the Impact of Ammonia-capturing Zeolite on Larval Development and Adult Phenotypic Quality

BackgroundVector control approaches that rely on mosquito releases such as the sterile insect technique (SIT) and suppression or replacement strategies relying on genetically modified mosquitoes (GMM) depend on effective mass production of Anopheles mosquitoes. For optimal development, Anophelines typically require relatively clean water which can be in short supply in some settings. Water replacement requires complex and onerous continuous-flow-systems and/or expensive water filtration systems like ultrafiltration and reverse osmosis. Thus, there is a need for simple cost-effective water management and treatment solutions. Zeolites are additives that have been extensively applied in fish and crustacean aquaculture to improve water quality because of their selective adsorption of ammonia and toxic heavy metals. The many advantages of zeolites include low cost, abundance in many parts of the world and their environmental friendliness, but so far they have not been exploited for mosquito rearing.MethodsThis study evaluated the independent effects of zeolite and daily water changes (to simulate a continuous flow system) on the rearing of An. coluzzii under two feed regimes (powder or solution feed) and larval densities (200 and 400 larvae per tray). The duration of larval development, adult emergence success and phenotypic quality (body size) were recorded to assess the impact of water treatments on mosquito numbers and phenotypic quality and to identify the optimal feeding regimes and density for zeolite use.ResultsOverall, mosquito emergence, duration of development and adult phenotypic quality was significantly better in treatments with daily water changes. In treatments without daily water changes, zeolite significantly improved water quality at the lower larval rearing density, resulting in higher mosquito emergence. Duration of development was significantly longer in zeolite treatments. At the lower larval rearing density, adult phenotypic quality did not significantly differ between zeolite treatment without water changes and those with daily changes. ConclusionsThese results suggest that treating rearing water with zeolite can improve mosquito production under some conditions, and thus offer a cheaper alternative to more expensive techniques such as ultrafiltration or reverse osmosis, which are often part of continuous water change systems. Further studies are needed to optimize its uses for rearing Anopheles gambiae s.l.