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Why are anopheline mosquitoes not present in the Seychelles?

Robert V, Rocamora G, Julienne S, Goodman SM - Malar. J. (2011)

Bottom Line: No evidence of larval or adult anophelines was found at the surveyed sites, which supports their absence in the Seychelles.In the southwestern atolls (Aldabra and Providence-Farquhar groups), the presence of a long dry season of up to nine months and the total absence of permanent natural freshwater prevents the breeding of anophelines and their successful colonization.The Seychelles does not have any native land mammals and like in other parts of the world (Antarctica, Iceland, New Caledonia, Central Pacific islands) their absence is associated with the lack of anophelines.

View Article: PubMed Central - HTML - PubMed

Affiliation: MIVEGEC Maladies infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle (IRD 224, CNRS 5290, Université Montpellier 1), Centre IRD France-Sud, BP 64501, 911 Avenue Agropolis, 34394 Montpellier cedex 5, France. vincent.robert@ird.fr

ABSTRACT

Background: Species of anopheline mosquitoes are largely distributed over emerged lands around the world and, within the tropics, few areas are without these insects, which are vectors of malaria parasites. Among the exceptions is the Seychelles archipelago in the western Indian Ocean. However, in the Aldabra island group, located in the extreme western portion of the archipelago, Anopheles gambiae s.l. was introduced, leading to massive proliferation and then elimination, with the most recent autochthonous malaria cases recorded in 1931.

Methods: In order to re-examine the absence of anopheline mosquitoes in the Seychelles, an entomological field survey was conducted in December 2008 at 17 sites on four granitic islands, including Mahé and Praslin, and ten sites on coralline atolls in the extreme west, including Aldabra.

Results: No evidence of larval or adult anophelines was found at the surveyed sites, which supports their absence in the Seychelles.

Conclusions: In the granitic islands of the Seychelles, the climate is favourable for anophelines. However, these islands are protected by their remoteness and prevailing seasonal winds. In addition, stagnant freshwater, required in anopheline larval development, is relatively uncommon on the granitic islands because of the steep slopes. In the southwestern atolls (Aldabra and Providence-Farquhar groups), the presence of a long dry season of up to nine months and the total absence of permanent natural freshwater prevents the breeding of anophelines and their successful colonization. The Seychelles does not have any native land mammals and like in other parts of the world (Antarctica, Iceland, New Caledonia, Central Pacific islands) their absence is associated with the lack of anophelines. This suggests an obligatory relationship for anophelines to feed on terrestrial mammals, without alternative for blood-feeding sources, such as bats, birds and reptiles.

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Photo of mosquito larvae collection, Aldabra Atoll, Picard Island. Note the larval breeding places are mainly natural and composed of coral rock pools inundated by rainwater. (Photo V.Robert/IRD).
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Figure 5: Photo of mosquito larvae collection, Aldabra Atoll, Picard Island. Note the larval breeding places are mainly natural and composed of coral rock pools inundated by rainwater. (Photo V.Robert/IRD).

Mentions: Entomological survey methods included: (i) Immature stages (larvae and pupae) - detailed examination for immature stages was performed at natural and human-made water collection sites, including marshes, tree holes, crab holes in mangroves, containers and reservoirs (Figure 5); (ii) Adult mosquitoes - using CDC Miniature Light Trap 6 volts (BioQuip™) from dusk to dawn, with a 4-watt incandescent light and a 4-watt black light tube (UV light ca. 320-420 nm). CDC traps were placed outdoors and used without olfactory attractant such as CO2 or next to human/animal bait. Systematic collection of mosquitoes on humans was not conducted, although alighting mosquitoes on members of the field team were collected. Netting of insects resting on vegetation was conducted only on Mahé, with few captures and these are not reported on herein.


Why are anopheline mosquitoes not present in the Seychelles?

Robert V, Rocamora G, Julienne S, Goodman SM - Malar. J. (2011)

Photo of mosquito larvae collection, Aldabra Atoll, Picard Island. Note the larval breeding places are mainly natural and composed of coral rock pools inundated by rainwater. (Photo V.Robert/IRD).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3045994&req=5

Figure 5: Photo of mosquito larvae collection, Aldabra Atoll, Picard Island. Note the larval breeding places are mainly natural and composed of coral rock pools inundated by rainwater. (Photo V.Robert/IRD).
Mentions: Entomological survey methods included: (i) Immature stages (larvae and pupae) - detailed examination for immature stages was performed at natural and human-made water collection sites, including marshes, tree holes, crab holes in mangroves, containers and reservoirs (Figure 5); (ii) Adult mosquitoes - using CDC Miniature Light Trap 6 volts (BioQuip™) from dusk to dawn, with a 4-watt incandescent light and a 4-watt black light tube (UV light ca. 320-420 nm). CDC traps were placed outdoors and used without olfactory attractant such as CO2 or next to human/animal bait. Systematic collection of mosquitoes on humans was not conducted, although alighting mosquitoes on members of the field team were collected. Netting of insects resting on vegetation was conducted only on Mahé, with few captures and these are not reported on herein.

Bottom Line: No evidence of larval or adult anophelines was found at the surveyed sites, which supports their absence in the Seychelles.In the southwestern atolls (Aldabra and Providence-Farquhar groups), the presence of a long dry season of up to nine months and the total absence of permanent natural freshwater prevents the breeding of anophelines and their successful colonization.The Seychelles does not have any native land mammals and like in other parts of the world (Antarctica, Iceland, New Caledonia, Central Pacific islands) their absence is associated with the lack of anophelines.

View Article: PubMed Central - HTML - PubMed

Affiliation: MIVEGEC Maladies infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle (IRD 224, CNRS 5290, Université Montpellier 1), Centre IRD France-Sud, BP 64501, 911 Avenue Agropolis, 34394 Montpellier cedex 5, France. vincent.robert@ird.fr

ABSTRACT

Background: Species of anopheline mosquitoes are largely distributed over emerged lands around the world and, within the tropics, few areas are without these insects, which are vectors of malaria parasites. Among the exceptions is the Seychelles archipelago in the western Indian Ocean. However, in the Aldabra island group, located in the extreme western portion of the archipelago, Anopheles gambiae s.l. was introduced, leading to massive proliferation and then elimination, with the most recent autochthonous malaria cases recorded in 1931.

Methods: In order to re-examine the absence of anopheline mosquitoes in the Seychelles, an entomological field survey was conducted in December 2008 at 17 sites on four granitic islands, including Mahé and Praslin, and ten sites on coralline atolls in the extreme west, including Aldabra.

Results: No evidence of larval or adult anophelines was found at the surveyed sites, which supports their absence in the Seychelles.

Conclusions: In the granitic islands of the Seychelles, the climate is favourable for anophelines. However, these islands are protected by their remoteness and prevailing seasonal winds. In addition, stagnant freshwater, required in anopheline larval development, is relatively uncommon on the granitic islands because of the steep slopes. In the southwestern atolls (Aldabra and Providence-Farquhar groups), the presence of a long dry season of up to nine months and the total absence of permanent natural freshwater prevents the breeding of anophelines and their successful colonization. The Seychelles does not have any native land mammals and like in other parts of the world (Antarctica, Iceland, New Caledonia, Central Pacific islands) their absence is associated with the lack of anophelines. This suggests an obligatory relationship for anophelines to feed on terrestrial mammals, without alternative for blood-feeding sources, such as bats, birds and reptiles.

Show MeSH
Related in: MedlinePlus