Anopheles culicifacies breeding in brackish waters in Sri Lanka and implications for malaria control

Abstract

BackgroundAnopheles culicifacies is the major vector of both falciparum and vivax malaria in Sri Lanka, while Anopheles subpictus and certain other species function as secondary vectors. In Sri Lanka, An. culicifacies is present as a species complex consisting of species B and E, while An. subpictus exists as a complex of species A-D. The freshwater breeding habit of An. culicifacies is well established. In order to further characterize the breeding sites of the major malaria vectors in Sri Lanka, a limited larval survey was carried out at a site in the Eastern province that was affected by the 2004 Asian tsunami.MethodsAnopheline larvae were collected fortnightly for six months from a brackish water body near Batticaloa town using dippers. Collected larvae were reared in the laboratory and the emerged adults were identified using standard keys. Sibling species status was established based on Y-chromosome morphology for An. culicifacies larvae and morphometric characteristics for An. subpictus larvae and adults. Salinity, dissolved oxygen and pH were determined at the larval collection site.ResultsDuring a six month study covering dry and wet seasons, a total of 935 anopheline larvae were collected from this site that had salinity levels up to 4 parts per thousand at different times. Among the emerged adult mosquitoes, 661 were identified as An. culicifacies s.l. and 58 as An. subpictus s.l. Metaphase karyotyping of male larvae showed the presence of species E of the Culicifacies complex, and adult morphometric analysis the presence of species B of the Subpictus complex. Both species were able to breed in water with salinity levels up to 4 ppt.ConclusionsThe study demonstrates the ability of An. culicifacies species E, the major vector of falciparum and vivax malaria in Sri Lanka, to oviposit and breed in brackish water. The sibling species B in the An. subpictus complex, a well-known salt water breeder and a secondary malaria vector in the country, was also detected at the same site. Since global warming and the rise in sea levels will further increase of inland brackish water bodies, the findings have significant implications for the control of malaria in Sri Lanka and elsewhere.

Salinity-tolerant larvae of mosquito vectors in the tropical coast of Jaffna, Sri Lanka and the effect of salinity on the toxicity of Bacillus thuringiensis to Aedes aegypti larvae

“…culicifacies s . l ., the major malaria vector in Sri Lanka, is recognized as a fresh water mosquito, it has been recently reported to undergo pre-imaginal development in brackish water of up to 4 ppt in eastern Sri Lanka [17]. The present findings show that this is also the case in the northern Jaffna district in Sri Lanka.…”

The dominant Anopheles vectors of human malaria in the Asia-Pacific region: occurrence data, distribution maps and bionomic précis

“…The bionomics and ecology of the species within this complex have been largely studied in India [23,241,251] and Sri Lanka [99,252,253], but there is a general lack of detailed information from other regions, especially the western areas [8]. Four species of the complex (A, C, D, E) are reportedly malaria vectors in India where they are apparently responsible for transmitting 60-65% of all cases of malaria in peri-urban and urban environments [254].…”

Anopheles culicifacies sibling species in Odisha, eastern India: First appearance of Anopheles culicifacies E and its vectorial role in malaria transmission

“…culicifacies E was identified for the first time in this study and was confirmed by molecular methods. This species is a highly competent vector for malaria globally and in India (Subbarao et al 1980(Subbarao et al , 1988Jude et al 2010).…”

“…culicifacies E has adapted to breed in diverse types of habitats such as brackish water in Sri Lanka like An. culicifacies B (Jude et al 2010). Its adaptability has enabled An.…”

“…Its adaptability has enabled An. culicifacies E to invade many areas, which were so far free from it; this is a matter of serious concern for vector control strategies (Jude et al 2010).…”