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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