Why are anopheline mosquitoes not present in the Seychelles?

Area of Science:

• Medical entomology
• Island biogeography
• Parasitology

Background:

• Anopheline mosquitoes, crucial vectors for malaria parasites, are globally distributed, yet absent from the Seychelles archipelago.
• An introduction of Anopheles gambiae s.l. to Aldabra island resulted in a temporary proliferation followed by elimination, with the last local malaria cases in 1931.

Purpose of the Study:

• To investigate the persistent absence of anopheline mosquitoes in the Seychelles.
• To identify ecological and environmental factors contributing to the lack of anopheline presence.

Main Methods:

• An entomological field survey was conducted in December 2008.
• Seventeen sites across four granitic islands (Mahé, Praslin) and ten sites on western coralline atolls (Aldabra) were surveyed.

Main Results:

• No larval or adult anopheline mosquitoes were detected at any of the surveyed locations.
• The findings confirm the absence of anophelines in the Seychelles.

Conclusions:

• Favorable climate on granitic islands is offset by remoteness, winds, and scarcity of freshwater habitats required for larval development.
• Southwestern atolls present long dry seasons and lack permanent freshwater, inhibiting anopheline breeding.
• The absence of anophelines correlates with the lack of native terrestrial mammals, suggesting a dependence on these hosts for blood-feeding.