Improvement of water quality for mass anopheline rearing: evaluation of the impact of ammonia-capturing zeolite on larval development and adult phenotypic quality

Abstract

Background Malaria vector 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. Anophelines typically require relatively clean larval rearing water, and water management techniques that minimise toxic ammonia are key to achieving optimal rearing conditions in small and large rearing facilities. Zeolites are extensively used in closed-system fish aquaculture to improve water quality and reduce water consumption, thanks to 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 environmental friendliness. However, so far, their potential benefit for mosquito rearing has not been evaluated. Methods This 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 and slurry 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, phenotypic quality and identification of optimal feeding regimes and larval density for the use of zeolite. Results Overall, mosquito emergence, duration of development and adult phenotypic quality were 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 and shorter development time. At the lower larval rearing density, the adult phenotypic quality did not significantly differ between zeolite treatment without water changes and those with daily changes. Conclusions These results suggest that treating rearing water with zeolite can improve mosquito production in smaller facilities. Zeolite could also offer cost-effective and environmentally friendly solutions for water recycling management systems in larger production facilities. Further studies are needed to optimise and assess the costs and benefits of such applications to Anopheles gambiae (s.l.) mosquito-rearing programmes. Graphic abstract

Physico-chemical characterization of Anopheles gambiae s.l. breeding sites and kdr mutations in urban areas of Cotonou and Natitingou, Benin

“…gambiae s.l populations to pyrethroids, observed in others countries in West Africa [47,48], is correlated with the high frequency of the Kdr L1014F mutation observed in the mosquitoes analyzed in the two cities. As in many other studies, this suggests that the Kdr mutation plays an important role in insecticide resistance of the pyrethroid family [38]. Furthermore, both species found in this study, namely An.…”

“…gambiae s.s. was the main species in the northern part. This species distribution can be explained by the varying climatic and environmental conditions as well as the ecological characteristics (physicochemical properties of larval habitats) provided by the cities [38]. An.…”

Characterization of Anopheles gambiae breeding sites and insecticide resistance mechanisms in urban areas of Cotonou and Natitingou, Benin

“…coluzzii had a higher tolerance to salinity than An. gambiae [39]. As one moves away from the coastal areas towards the inland regions, the salt content in larval habitats decreases, which could explain the progressive decrease in the proportions of An.…”