Reverse osmosis and ultrafiltration for recovery and reuse of larval rearing water in Anopheles arabiensis mass production: Effect of water quality on larval development and fitness of emerging adults

Improvement of water quality for mass anopheline rearing: dynamics of larval tray bacterial communities under different water treatments revealed by 16S ribosomal RNA amplicon sequencing

BACKGROUND

Immature anophelines inhabit aquatic environments with diverse physicochemical properties and microorganisms. In insectary settings, ammonia accumulation in larval rearing trays can lead to high larval mortality. Bacterial communities in these trays may influence ammonia levels through nitrification and denitrification. While symbiotic bacteria are known to be crucial for nutrition, digestion, reproduction, and immune responses in anophelines, the microbial communities specifically associated with Anopheles coluzzii larvae have not been characterised.

METHODS AND RESULTS

Building on a study examining ammonia-capturing zeolite and water changes for rearing Anopheles coluzzii, this research characterised the bacterial communities using 16S rRNA gene sequencing to identify species linked to larval survival and phenotypic quality. Functional filters were applied to identify bacteria related to ammonia nitrification and their impact on larval development. qPCR was used to validate the sequencing data for the 10 most significant bacteria. Water changes significantly reduced bacterial diversity and abundance, improving adult mosquito development and quality. In contrast, untreated trays showed a higher abundance of potentially harmful bacteria, adversely affecting development. Applying zeolite increased nitrifying bacteria presence, benefiting mosquito growth while lowering toxic bacteria levels-trends confirmed by qPCR.

CONCLUSIONS

This study offers insights into the bacterial communities in mosquito larval-rearing water, highlighting species that could enhance ammonia nitrification and overall rearing success.

Combined effect of physico-chemical and microbial quality of breeding habitat water on oviposition of malarial vector Anopheles subpictus

Mosquitoes prefer diverse water bodies for egg laying and larval survival. Present study was performed with an objective to characterize physico-chemical properties and microbial profiling of breeding habitat water bodies of Anopheles subpictus mosquitoes. A field survey was accomplished to check the presence of An. subpictus larvae to record per dip larval density in various breeding habitats throughout the year. Physico-chemical and bacteriological properties in relation to mosquito oviposition were assessed. Dissolved oxygen content, pH and alkalinity were found to have major impacts and ponderosity on the prevalence of An. subpictus larvae. Larval density showed significant positive correlation with dissolved oxygen content of water and significant negative correlation with pH and alkalinity of habitat water. Comparatively higher population (cfu/mL) of Bacillus spp. competent with starch hydrolyzing and nitrate reducing properties were recorded all the breeding habitat water bodies of An. subpictus. Higher amplitude of anopheline larvae was portrayed during monsoon and post-monsoon season in clear water with an inclining trend to high dissolved oxygen content and neutral pH. B. cereus, B. megaterium, B. subtilis and B. tequilensis prevalent in all habitat water bodies were marked as oviposition attractants of gravid An. subpictus mosquitoes. Microbial population played key roles in the modulation of physico-chemical parameters of habitat water with a view to enhance its acceptability by gravid mosquitoes in relation to their oviposition. Better understanding of the interactions along with the control of oviposition attractant bacterial strains from mosquito breeding habitats might contribute to the vector management programme.

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

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

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04763-w.

The Insect Pest Control Laboratory of the Joint FAO/IAEA Programme: Ten Years (2010-2020) of Research and Development, Achievements and Challenges in Support of the Sterile Insect Technique

The Joint FAO/IAEA Centre (formerly called Division) of Nuclear Techniques in Food and Agriculture was established in 1964 and its accompanying laboratories in 1961. One of its subprograms deals with insect pest control, and has the mandate to develop and implement the sterile insect technique (SIT) for selected key insect pests, with the goal of reducing the use of insecticides, reducing animal and crop losses, protecting the environment, facilitating international trade in agricultural commodities and improving human health. Since its inception, the Insect Pest Control Laboratory (IPCL) (formerly named Entomology Unit) has been implementing research in relation to the development of the SIT package for insect pests of crops, livestock and human health. This paper provides a review of research carried out between 2010 and 2020 at the IPCL. Research on plant pests has focused on the development of genetic sexing strains, characterizing and assessing the performance of these strains (e.g., Ceratitis capitata), elucidation of the taxonomic status of several members of the Bactrocera dorsalis and Anastrepha fraterculus complexes, the use of microbiota as probiotics, genomics, supplements to improve the performance of the reared insects, and the development of the SIT package for fruit fly species such as Bactrocera oleae and Drosophila suzukii. Research on livestock pests has focused on colony maintenance and establishment, tsetse symbionts and pathogens, sex separation, morphology, sterile male quality, radiation biology, mating behavior and transportation and release systems. Research with human disease vectors has focused on the development of genetic sexing strains (Anopheles arabiensis, Aedes aegypti and Aedes albopictus), the development of a more cost-effective larvae and adult rearing system, assessing various aspects of radiation biology, characterizing symbionts and pathogens, studying mating behavior and the development of quality control procedures, and handling and release methods. During the review period, 13 coordinated research projects (CRPs) were completed and six are still being implemented. At the end of each CRP, the results were published in a special issue of a peer-reviewed journal. The review concludes with an overview of future challenges, such as the need to adhere to a phased conditional approach for the implementation of operational SIT programs, the need to make the SIT more cost effective, to respond with demand driven research to solve the problems faced by the operational SIT programs and the use of the SIT to address a multitude of exotic species that are being introduced, due to globalization, and established in areas where they could not survive before, due to climate change.

Does Tap Water Quality Compromise the Production of Aedes Mosquitoes in Genetic Control Projects?

Simple Summary

Scientists all over the world are continually rearing and producing insects in laboratories for many purposes including pest control programmes. Aedes aegypti and Ae. albopictus are mosquitoes of public health importance due to their ability to vector human and animal pathogens and thus vector control represents an important component of many disease control programmes. Water is a factor of great importance in the larval environment of mosquito species. However, obtaining sufficient water of reliable quality for mosquito rearing is still challenging, especially in developing and least developed countries, where access even to clean drinking water is limited. In prospect of cost-effective methods for improved mass-rearing toward SIT application, we assessed the impact of using tap water on the development and quality of Aedes mosquitoes. Results showed that, tap water with hardness/electrical conductivity beyond certain levels (140 mg/l CaCO₃ or 368 µS/cm) was shown to have a negative impact on the production of Ae. albopictus and Ae. aegypti mosquitoes. These results suggest that the quality of water should be checked when using for rearing mosquitoes for release purposes in order to optimize the production performance of mass-rearing facilities. This may have important implications for the implementation of the sterile insect technique in areas where reverse osmosis water is a scarce or costly resource.

Abstract

A mosquito’s life cycle includes an aquatic phase. Water quality is therefore an important determinant of whether or not the female mosquitoes will lay their eggs and the resulting immature stages will survive and successfully complete their development to the adult stage. In response to variations in laboratory rearing outputs, there is a need to investigate the effect of tap water (TW) (in relation to water hardness and electrical conductivity) on mosquito development, productivity and resulting adult quality. In this study, we compared the respective responses of Aedes aegypti and Ae. albopictus to different water hardness/electrical conductivity. First-instar larvae were reared in either 100% water purified through reverse osmosis (ROW) (low water hardness/electrical conductivity), 100% TW (high water hardness/electrical conductivity) or a 80:20, 50:50, 20:80 mix of ROW and TW. The immature development time, pupation rate, adult emergence, body size, and longevity were determined. Overall, TW (with higher hardness and electrical conductivity) was associated with increased time to pupation, decreased pupal production, female body size in both species and longevity in Ae. albopictus only. However, Ae. albopictus was more sensitive to high water hardness/EC than Ae. aegypti. Moreover, in all water hardness/electrical conductivity levels tested, Ae. aegypti developed faster than Ae. albopictus. Conversely, Ae. albopictus adults survived longer than Ae. aegypti. These results imply that water with hardness of more than 140 mg/l CaCO₃ or electrical conductivity more than 368 µS/cm cannot be recommended for the optimal rearing of Aedes mosquitoes and highlight the need to consider the level of water hardness/electrical conductivity when rearing Aedes mosquitoes for release purposes.