8 research outputs found
Laboratory and microcosm experiments reveal contrasted adaptive responses to ammonia and water mineralisation in aquatic stages of the sibling species Anopheles gambiae (sensu stricto) and Anopheles coluzzii
Get PDF© The Author(s) 2021Background: The sibling species of the malaria mosquito, Anopheles gambiae (sensu stricto) and Anopheles coluzzii co-exist in many parts of West Africa and are thought to have recently diverged through a process of ecological speciation with gene flow. Divergent larval ecological adaptations, resulting in Genotype-by-Environment (G × E) interactions, have been proposed as important drivers of speciation in these species. In West Africa, An. coluzzii tends to be associated with permanent man-made larval habitats such as irrigated rice fields, which are typically more eutrophic and mineral and ammonia-rich than the temporary rain pools exploited by An. gambiae (s.s.).
Methods: To highlight G × E interactions at the larval stage and their possible role in ecological speciation of these species, we first investigated the effect of exposure to ammonium hydroxide and water mineralisation on larval developmental success. Mosquito larvae were exposed to two water sources and increasing ammonia concentrations in small containers until adult emergence. In a second experiment, larval developmental success was compared across two contrasted microcosms to highlight G × E interactions under conditions such as those found in the natural environment.
Results: The first experiment revealed significant G × E interactions in developmental success and phenotypic quality for both species in response to increasing ammonia concentrations and water mineralisation. The An. coluzzii strain outperformed the An. gambiae (s.s.) strain under limited conditions that were closer to more eutrophic habitats. The second experiment revealed divergent crisscrossing reaction norms in the developmental success of the sibling species in the two contrasted larval environments. As expected, An. coluzzii had higher emergence rates in the rice paddy environment with emerging adults of superior phenotypic quality compared to An. gambiae (s.s.), and vice versa, in the rain puddle environment.
Conclusions: Evidence for such G × E interactions lends support to the hypothesis that divergent larval adaptations to the environmental conditions found in man-made habitats such as rice fields in An. coluzzii may have been an important driver of its ecological speciation.This work was funded by a PhD scholarship from Faculty for the Future fellowship, Schlumberger Foundation, The Hague, The Netherlands, and Niger Delta Development Commission, Nigeria, to N.O.A
Improvement of water quality for mass anopheline rearing: evaluation of the impact of ammonia-capturing zeolite on larval development and adult phenotypic quality
Get PDF© The Author(s) 2021.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.This work was funded by a PhD scholarship from the Faculty for the Future fellowship, Schlumberger Foundation, The Hague, The Netherlands, and Niger Delta Development Commission, Nigeria, to NOA
Effect of water source and feed regime on development and phenotypic quality in Anopheles gambiae (s.l.): prospects for improved mass-rearing techniques towards release programmes
Get PDF© The Author(s) 2019.BACKGROUND: In many malaria-endemic sub-Saharan countries, insecticide resistance poses a threat to existing mosquito control measures, underscoring the need for complementary control methods such as sterile and/or genetically-modified mosquito release programmes. The sibling species Anopheles gambiae and An. coluzzii are responsible for malaria transmission in most of this region. In their natural habitat, these species generally breed in clean, soft water and it is believed that divergent preference in their larval breeding sites have played a role in their speciation process. Mosquito release programmes rely on the rearing of mosquitoes at high larval densities. Current rearing protocols often make use of deionised water regardless of the strain reared. They also depend on a delicate balance between the need for adequate feeding and the negative effect of toxic ammonia and food waste build-up on mosquito development, making managing and improving water quality in the insectary imperative.
METHODS: Here, we investigated the impact of water source and feed regimes on emergence rate and phenotypic quality of mosquitoes in the insectary. First-instar larvae of An. gambiae (Kisumu strain) and An. coluzzii (Mopti and VK3 strains) were reared in three water sources with varying degrees of hardness (deionised, mineral and a mix of the two), with a daily water change. Larvae were fed daily using two standardised feeding regimes, solution and powder feed.
RESULTS: Water source had a significant impact on mosquito size and development time for all strains. Earlier emergence of significantly larger mosquitoes was observed in mineral water with the smallest mosquitoes developing later from deionised water. Wing-length was significantly longer in mineral, mixed water and in powder feed, irrespective of sex, strains or water types. Deionised water was the least favourable for mosquito quality across all strains.
CONCLUSIONS: Mineral water and powder feed should be used in rearing protocols to improve mosquito quality where the optimal quality of mosquitoes is desired. Although results obtained were not significant for improved mosquito numbers, the phenotypic quality of mosquitoes reared was significantly improved in mineral water and mix water. Further studies are recommended on the impact mineral water has on other fitness traits such as longevity, fecundity and mating competitiveness.This work was funded by a PhD scholarship from Faculty for the Future fellowship, Schlumberger Foundation, The Hague, Netherlands and Niger Delta Development Commission, Nigeria to N.O.A
Current status of Glossina population ecology
Get PDF© 2015 Okiwelu et al.BACKGROUND: Vector control remains the most visible method for large scale control of trypanosomiasis; there is a lack of suitable prophylactic drugs and vaccines against trypanosomiases and chemotherapeutic agents remain too expensive and dangerous for most people in endemic areas. Glossina populations are the target units and therefore an in-depth understanding of their ecology is a pre-requisite to the development of effective control measures.
SAMPLING METHODS: Refers to methods of catching tsetse flies in the field. Earlier Researchers utilized walking parties to catch flies or standing catch with hand nets. Studies in the 1970s highlighted the shortcomings of these methods. A variety of traps has since been developed for diverse species.
POPULATION DYNAMICS: Refers to changes in population abundance over time. Three processes (dispersal, natality, mortality) are involved in determining population levels. Geographic structure is the distribution and abundance within and among populations. Based on direct observations, mark-recapture protocols or radio-tracking, earlier view was that Glossina dispersal was random. Currently, the best available description is a diffusion process; flies at the margins of the distributional range begin the process, which gradually moves inwards. Calculation of growth rates is easier for small closed Glossina populations. There is a consensus among tsetse ecologists that both density-dependent and density-independent factors are important in the regulation of tsetse numbers.
POPULATION GENETICS: It encompasses two distinct but related components: demographic and genetic distribution of genetic variation and the result of migration, selection mutation, genetic drift and related factors: New molecular genetics techniques have allowed insights into many fields.
CONCLUSION: There have been significant advances in Glossina ecology over the past 3 decades. These have been possible because of the availability of comprehensive data from long-term field studies and the introduction of new molecular genetics techniques that have allowed insights into many fields. Glossina population genetics and manipulation of prokaryotic symbiont species may provide avenues for management innovations to confront the intractable problem of trypanosomiasis in Africa.Unfunde
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
Get PDF© The Author(s) 2025. Published by Oxford University Press on behalf of Applied Microbiology International.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 ten 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.This work was supported by a PhD scholarship from Faculty for the Future fellowship, Schlumberger Foundation, The Hague, Netherlands, and Niger Delta Development Commission, Nigeria to N.O.
Effect of water source and feed regime on development and phenotypic quality in Anopheles gambiae (s.l.): prospects for improved mass-rearing techniques towards release programmes
Get PDFAbstract Background In many malaria-endemic sub-Saharan countries, insecticide resistance poses a threat to existing mosquito control measures, underscoring the need for complementary control methods such as sterile and/or genetically-modified mosquito release programmes. The sibling species Anopheles gambiae and An. coluzzii are responsible for malaria transmission in most of this region. In their natural habitat, these species generally breed in clean, soft water and it is believed that divergent preference in their larval breeding sites have played a role in their speciation process. Mosquito release programmes rely on the rearing of mosquitoes at high larval densities. Current rearing protocols often make use of deionised water regardless of the strain reared. They also depend on a delicate balance between the need for adequate feeding and the negative effect of toxic ammonia and food waste build-up on mosquito development, making managing and improving water quality in the insectary imperative. Methods Here, we investigated the impact of water source and feed regimes on emergence rate and phenotypic quality of mosquitoes in the insectary. First-instar larvae of An. gambiae (Kisumu strain) and An. coluzzii (Mopti and VK3 strains) were reared in three water sources with varying degrees of hardness (deionised, mineral and a mix of the two), with a daily water change. Larvae were fed daily using two standardised feeding regimes, solution and powder feed. Results Water source had a significant impact on mosquito size and development time for all strains. Earlier emergence of significantly larger mosquitoes was observed in mineral water with the smallest mosquitoes developing later from deionised water. Wing-length was significantly longer in mineral, mixed water and in powder feed, irrespective of sex, strains or water types. Deionised water was the least favourable for mosquito quality across all strains. Conclusions Mineral water and powder feed should be used in rearing protocols to improve mosquito quality where the optimal quality of mosquitoes is desired. Although results obtained were not significant for improved mosquito numbers, the phenotypic quality of mosquitoes reared was significantly improved in mineral water and mix water. Further studies are recommended on the impact mineral water has on other fitness traits such as longevity, fecundity and mating competitiveness
Effect of water source and feed regime on development and phenotypic quality in Anopheles gambiae (s.l.): prospects for improved mass-rearing techniques towards release programmes
No full textEntomological baseline data collection and power analyses in preparation of a mosquito swarm-killing intervention in south-western Burkina Faso
No full textAbstract
Background
Insecticides are currently the main tools used to reduce the transmission of malaria; therefore, the development of resistance to insecticides in malaria vectors is of major concern for malaria control. The resistance level to pyrethroids is particularly high in the Western region of Burkina Faso and may affect the efficacy of insecticidal bed nets and indoor residual spraying. Adult mosquito swarming and other nocturnal behaviours exhibit spatial and temporal patterns that suggest potential vulnerability to targeted space spraying with effective insecticides. Indeed, targeted space-spraying against adult mosquito swarms has been used to crash mosquito populations and disrupt malaria transmission.
Methods
Prior to impact assessment of swarm killing, a baseline data collection was conducted from June to November 2016 in 10 villages divided into two areas in western Burkina Faso. The data considered both ecological and demographic characteristics to monitor the key entomological parameters.
Results
The mean number of swarms observed was 35 per village, ranging from 25 to 70 swarms according to the village. Female density in both areas varied significantly as a function of the village and the period of collection. The human biting rate was significantly affected by the period of collection and depended upon whether the collection was carried out indoors or outdoors. Averages of parity rate were high in both areas for all periods of collection, ranging from 60 to 90%. These values ranged from 80 to 100% for inseminated females. Sporozoite rates ranged between 1.6 and 7.2% depending upon the village. The molecular identification of resting and swarming mosquitoes showed the presence of the three major malaria vectors in Burkina Faso, but in different proportions for each village.
Conclusions
The distribution of the potential swarm markers and swarms in villages suggested that swarms are clustered across space, making intervention easier. Power simulations showed that the direct sampling of swarms provides the highest statistical power, thereby reducing the number of villages needed for a trial.
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