The ecological role of mosquito larvae in aquatic environments

The ecological role of mosquito larvae in aquatic environments

The ecological role of mosquito larvae in aquatic environments

Assessing the community role and trophic interactions of Anopheles gambiae larvae in the Volta Region of Ghana.

IMAGE CREDIT: Michelle L. D’Souza

 The Anopheles gambiae mosquito complex, which consists of eight species, is the prevalent malaria vector in Sub-Saharan Africa1. While we have a reasonable understanding of predation rates, resource availability, and competition among aquatic invertebrate2-7, we lack a comprehensive appreciation of the larval ecology of An. gambiae, including their trophic role, diets, and population dynamics. My research aims to address this gap, crucial in integrating aquatic habitat management with vector control programs8.

With the advance of DNA technologies such as metabarcoding, we can now identify prey to a species level by examining the stomach contents of aquatic predators. When using these insights with network analyses, it is possible to quantify direct and indirect ecological interactions in the environment9. I will take advantage of these techniques for my research which aims to assess the trophic interactions of An. gambiae larvae in water bodies within two agricultural communities in Ghana.

I will collect mosquito larvae with a dipper, and a larger subset of invertebrates with an aquatic net (with a mesh size of 250 μm).  Each specimen’s gut contents will be analyzed using DNA barcoding and this data will be used to gain an understanding of the larval niche and ultimately An. gambiae’s role within the aquatic community. I will examine network interaction metrics such as connectance (the number of realized connections between species relative to what is available), degree (the number of interaction partners), betweenness (the importance of a species as a connector between different groups), and closeness (how central a focal species is in the community) to aid in niche construction. Temperature, pH, dissolved oxygen, salinity, and conductivity of the target water bodies will also be measured while sampling as these factors affect the occurrence and abundance of larvae by influencing the breeding behaviours of mosquitoes10.

In addition, I plan to study how different species of mosquito larvae compete for key resources. In the laboratory, the densities of local-caught larval populations of An. gambiae and other mosquito species will be manipulated to help determine the strongest competitor. While maintaining optimal rearing conditions by measuring the physio-chemical properties of the water daily, I will examine four indicators of overall growth and survival (the mean time to pupation, percentage of larvae that did not reach the adult stage, sex ratio, and mean female wing length) and therefore infer competitive strength among species. These data will provide important insights into predicting whether another mosquito species would dominate if the number of An. gambiae is reduced in the habitat.

An. gambiae is relatively small, constituting about half to one-third the mass of many Aedes mosquito species12. Foraging theory indicates that small, mobile insects of low profitability, do not form a preferred food source to predators unless they are massively clustered13. Though many species feed on mosquitos, these animals also feed on other small organisms that typically co-occur with An. gambiae14. For these reasons, I do not foresee that An. gambiae larvae will be a key food source for any predator in the aquatic environments in Ghana or that they will have a central role in local trophic systems.

If this is proven to be true, it will provide evidence that malaria-intervention methods that aim to suppress or reduce An. gambiae mosquitoes will not have detrimental consequences for the larger community.

Written by

Afia S. Karikari

Afia S. Karikari

African Regional Postgraduate Programme in Insect Science, University of Ghana, Accra, Ghana  

April 21, 2021

doi:10.21083/ibol.v11i1.6619 

This research is part of a larger effort by Target Malaria in Ghana to understand the role of the An. gambiae mosquito in the broader ecosystem.

For more information see:

The important interactions behind the itch

References:

  1. Service MW (1971) Studies on sampling larval populations of the Anopheles gambiae Bulletin of the World Health Organization 45:169–180.
  2. Service MW (1973) Mortalities of the larvae of the Anopheles gambiae Giles complex and detection of predators by the precipitin test. Bulletin of Entomological Research 62:359– 369.
  3. Service MW (1977) Mortalities of the immature stages of species of the Anopheles gambiae complex in Kenya: comparison between rice fields and temporary pools, identification of predators, and effects of insecticidal spraying. Journal of Medical Entomology 13:535–545.
  4. Ho BC, Ewert A, Chew LM (1989) Interspecific competition among Aedes Aegypti, albopictus and Ae. triseriatus (Diptera: Culicidae). Journal of Medical Entomology. 26:615–623.
  5. Barrera L (1996) Competition and resistance to starvation in larvae of container-inhabiting Aedes mosquitos. Ecological Entomology 21:117–127.
  6. Juliano SA, Lounibos LP and O’Meara GF (2004) A field test for competitive effects of Aedes albopictus on aegypti in south Florida: differences between sites and co-existence and exclusion? Oecologia. 139:583–593.
  7. Braks MAH, Honόrio NA, Lounibos LP, Lourenςo-de-Oliveira R, Juliano SA (2004) Interspecific competition between two invasive species of container mosquitos, Aedes aegypti and Aedes albopictus (Diptera: Culicidae), in Brazil. Annual Entomological Society of America 97:130–139.
  8. Li L, Bian L, Yakob L, Zhou U, Yan G (2009) Temporal and spatial stability of Anopheles gambiaelarval habitat distribution in western Kenya highlands. International Journal of Health Geographics. 8(70). doi:10.1186/1476-072X-8-70
  9. Fath BD, Patten BC (1998) Network synergism: emergence of positive relations in ecological systems. Ecological Modelling 107:127–143.
  10. Clements AN (1992) The Biology of Mosquitoes (Vol 1) Development, Nutrition and Reproduction. Chapman and Hall, London.
  11. Paajimans KP, Huijben S, Githeko AK, Takken W (2009) Competitive interactions between larvae of the malaria mosquitos, Anopheles arabiensis and Anopheles gambiae under semi-field conditions in western Kenya. Acta Tropica. 109:124–
  12. Koella JC, Lyimo EO (1996) Variability in the relationship between weight and wing length of Anopheles gambiae (Diptera: Culicidae). Journal of Medical Entomology 33: 261–264.
  13. Stephens DW, Brown JS, Ydenberg RC (2007) Foraging: Behavior and Ecology. University of Chicago Press, Chicago, IL.
  14. Findley JS, Black H (1983) Morphological and dietary structuring of a Zambian insectivorous bat community. Ecology 64:625–630.

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What we know, don’t know, and think we know about the predators of mosquitoes

What we know, don’t know, and think we know about the predators of mosquitoes

What we know, don’t know, and think we know about the predators of mosquitoes

Studying ecological relationships and community perceptions of Anopheles gambiae (Diptera: Culicidae) and their predators

IMAGE CREDIT: Michelle L. D’Souza

 The malaria-transmitting mosquito An. gambiae is eaten by species of bats, birds, damselflies, dragonflies, and spiders, although the mosquito likely accounts for only a small percentage of their total diet1. While there is limited data on the predation of adult An. gambiae at blood-feeding, nectar-feeding, and breeding sites, my research will use DNA metabarcoding techniques combined with ecological network analyses to determine the diet of predators and the community structure of predator-prey interactions.

Currently, we lack an understanding of indigenous perceptions surrounding An. gambiae. While Ghana’s local communities have expressed an interest in sharing their first-hand knowledge on various problems associated with mosquitoes, researchers often fail to consult them. Local peoples’ perceptions, knowledge, and experiences of the ecological relationship between predators and mosquitoes in the area where they live and farm provide important information to consider when addressing misconceptions that could impede malaria control interventions2.

My research will group mosquito activities into feeding (e.g., blood-feeding and nectar-feeding) and breeding (e.g., oviposition and eclosion) behaviours upon sampling specimens at three site types: (1) in homes both indoors and outdoors, (2) near vegetation and flowering plants closer to homes, and (3) around clear and shallow temporary water bodies.

I will sample invertebrates using both active and passive sampling traps including Malaise traps, pitfall traps, yellow pan traps, light traps, sweep nets, and aerial nets. Insectivorous invertebrates will be sorted out from the total trap catch and their diet composition determined by DNA metabarcoding to identify mosquitoes as well as other prey. I will also ascertain whether the diet of a predator changes with the sampling site, for example, where An. gambiae is feeding or depositing eggs. I will further determine how the predators are distributed across sampling sites, and in which of the sampling sites An. gambiae is most vulnerable to predation. I will analyze the invertebrate community coexisting with adult An. gambiae and the community structure of predator-prey interactions by using ecological network analysis, thus determining the role of An. gambiae in the food web.   

To assess indigenous knowledge and local perceptions on the ecological role of An. gambiae, I plan to distribute questionnaires that will gather basic information on mosquito identification, biology, and ecology as well as observations on feeding interactions and locations, and the predators involved. Questionnaire results will be compared with those of the metabarcoding results to determine the presence and extent of misconceptions regarding predatory interactions.

My goal is to assess the extent of mosquito knowledge in the community so that I can design appropriate education measures to ensure that future vector control projects are successful. The local communities’ knowledge and understanding of mosquito ecology is vital in these efforts.

This research will fill knowledge gaps regarding the role of An. gambiae in the local ecosystem and also help predict any possible ecological consequences of suppressing the malaria-transmitting mosquito as part of a vector control strategy.

Written by

Roger Sigismund Anderson

Roger Sigismund Anderson

African Regional Postgraduate Programme in Insect Science, University of Ghana, Ghana  

April 12, 2021

doi:10.21083/ibol.v11i1.6597

This research is part of a larger effort by Target Malaria in Ghana to understand the role of the An. gambiae mosquito in the broader ecosystem.

For more information see:

The important interactions behind the itch

References:

1. Collins CM, Bonds JAS, Quinlan MM, & Mumford JD (2019) Effects of the removal or reduction in density of the malaria mosquito, Anopheles gambiae s.l., on interacting predators and competitors in local ecosystems. Medical and Veterinary Entomology, 33(1), 1-15.

2. Ahorlu CK, Dunyo SK, Afari EA, Koram KA & Nkrumah FK (1997) Malaria‐related beliefs and behaviour in southern Ghana: implications for treatment, prevention and control. Trop Med Int Health 2, 488–499.

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Ecological and epidemiological insights from blood meals

Ecological and epidemiological insights from blood meals

Ecological and epidemiological insights from blood meals

Using interaction networks to explore the community structure and network ecology of biting insects and their hosts
PHOTO CREDIT: Ben Bellekom, IMAGE CREDIT: Michelle L. D’Souza

Knowledge of variations in insect biting behaviour and feeding patterns of insect disease vectors is important in understanding disease epidemiology and establishing effective control methods. Blood feeding insects are embedded within complex ecological communities and interact with other species acting as predator, prey, or competitor. These interactions are likely to impact the population dynamics of those co-occurring species1.

Biting insects exist within a variety of landscapes, where landscape change is likely to influence host-insect interactions2,3.  For example, deforestation within the Peruvian Amazon resulted in 278 times more human interactions with the malaria vector Anopheles darlingi than in undisturbed habitat, leading to a rise in malaria transmission4. Consequently, creating vector controls requires an understanding of how the landscape modifies biting insect community structure and biting interaction frequencies. Similarly, community structure, host availability, and the frequency of interactions may all be affected by time, again with consequences for disease transmission.  For example, the Leishmaniasis vector, sand flies, are most active at dawn and dusk, with a resultant increase in transmission risk to nocturnal hosts5.

Biting insect research has primarily focused on the analysis of single biting insect species or small sets of interacting species to examine host usage and to screen vectors for pathogens of interest (such as Zika virus and malaria). As many biting insects are medically important, research has also focused on the effects of specific control initiatives, such as examining Anopheles mosquito abundances following the implementation of long-lasting insecticidal nets. Whilst limited work has examined the effect of habitat modification and temporal variations on feeding patterns and species abundances, this work has broadly overlooked the community aspect6. Therefore, there is currently an incomplete understanding of the degree to which these variations and distance from human habitation7, impact interaction frequencies, and the structural properties of the wider biting insect-host community. Indeed, as insect communities themselves are rarely studied, the full ecological and epidemiological implications of their interactions is currently unknown, so that the design of control strategies is potentially compromised.

Understanding such interactions is possible by constructing interaction networks, which provide a visual and mathematical representation of a community of species, connected through their feeding interactions8,9. I will create biting insect-host interaction networks using data from insect bloodmeals, focusing on the communities of biting flies in Ghana. I will explore the impact of landscape, comparing distinct habitat categories (such as scrubland and fallow land), and temporal variations (day or night), and the effect of proximity to human habitation on biting insect-host community composition, structural properties, such as how specialised the network is, and relative species’ abundances. I will use metabarcoding to create data on species interactions as it allows for the identification of animal DNA in a mixed sample collected from biting insect bloodmeals10.

I have augmented this fieldwork with a literature-based analysis of published blood meal interaction data. This provides an in-depth opinion on the value of interaction networks in understanding host-insect-disease interactions and highlights their future applications in identifying and monitoring emerging diseases and unrecognized vectors11. Further, using a global data set extracted from the literature, I aim to examine structural variations of biting insect-host communities between distinct habitat types and latitudes. The results generated by my work will provide valuable insight into biting insect community ecology, evaluate the potential impact of interventions on community structure and interactions.

Written by

Ben Bellekom

Ben Bellekom

Department of Zoology, University of Oxford, Oxford, UK

February 24, 2021

doi:10.21083/ibol.v11i1.6539

This research is part of a larger effort by Target Malaria in Ghana to understand the role of the An. gambiae mosquito in the broader ecosystem.

For more information see:

The important interactions behind the itch

References:

1. Ferguson HM, Dornhaus A, Beeche A, Borgemeister C, Gottlieb M, Mulla MS, Gimnig J, Fish D, Kileen G (2010) Ecology: A prerequisite for malaria elimination and eradication. PLOS Medicine 7. doi:10.1371/journal.pmed.1000303

2. Wolinska J, King KC (2009) Environment can alter selection in host-parasite interactions. Trends in Parasitology 25: 236–244. doi:10.1016/j.pt.2009.02.004

3. Lachish S, Knowles S, Alves R, Sepil I, Davies A, Lee S, Wood M, Sheldon B (2013) Spatial determinants of infection risk in a multi-species avian malaria system. Ecography 36:587–598. doi:10.1111/j.1600-0587.2012.07801.x

4. Vittor AY, Gilman RH, Tielsch J, Glass G, Shields T, Lozano WS, Pinedo-Cancino V, Patz J (2006) The effect of deforestation on the human-biting rate of Anopheles darlingi, the primary vector of falciparum malaria in the Peruvian Amazon. American Journal of Tropical Medicine and Hygiene 74:3–11. doi:10.4269/ajtmh.2006.74.3

5. Aklilu E, Gebresilassie A, Yared S, Kindu M, Tekie H, Balkew M, Warburg A, Hailu A, Gebre-Michael T (2017) Comparative study on the nocturnal activity of phlebotomine sand flies in a highland and lowland foci of visceral leishmaniasis in north-western Ethiopia with special reference to Phlebotomus orientalis. Parasites & Vectors 10:393. doi:0.1186/s13071-017-2339-6

6. Braack L, Almeida P, Cornel A, Swanepoel R, de Jager C (2018) Mosquito-borne arboviruses of African origin: review of key viruses and vectors. Parasites & Vectors 11:29. doi:10.1186/s13071-017-2559-9

7. Orsborne, J, Furuya-Kanamori L, Jeffries C, Kristan M, Mohammed A, Afrane Y, O’Reilly K, Massad E, Drakeley C, Walker T, Yakob L (2019) Investigating the blood-host plasticity and dispersal of Anopheles coluzzii using a novel field-based methodology. Parasites & Vectors 12:143. doi:10.1186/s13071-019-3401-3

8. Kaiser-Bunbury C.N, Blüthgen N (2015) Integrating network ecology with applied conservation: a synthesis and guide to implementation. AoB Plants 7. doi:10.1093/aobpla/plv076

9. Proulx S.R, Promislow D, Phillips P (2005) Network thinking in ecology and evolution, Trends in Ecology & Evolution 20:345–353. https://doi.org/10.1016/j.tree.2005.04.004

10. Drinkwater R, Schnell I, Bohmann K, Bernard H, Veron G, Clare E, Gilbert T, Rossiter S (2019) Using metabarcoding to compare the suitability of two blood‐feeding leech species for sampling mammalian diversity in North Borneo, Molecular Ecology Resources 19:105–117. doi:10.1111/1755-0998.12943

11. Bellekom B, Hackett TD, Lewis OT (2021) A network perspective on the vectoring of human disease. Trends in Parasitology. doi: 10.1016/j.pt.2020.12.001

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