Biological differences between brackish and fresh water-derived Aedes aegypti from two locations in the Jaffna peninsula of Sri Lanka and the implications for arboviral disease transmission.

Ranjan Ramasamy,Pavilupillai J Jude,Thabothiny Veluppillai,Thampoe Eswaramohan,Sinnathamby N Surendran,Immo A Hansen

doi:10.1371/journal.pone.0104977

Abstract

The mainly fresh water arboviral vector Aedes aegypti L. (Diptera: Culicidae) can also undergo pre-imaginal development in brackish water of up to 15 ppt (parts per thousand) salt in coastal areas. We investigated differences in salinity tolerance, egg laying preference, egg hatching and larval development times and resistance to common insecticides in Ae. aegypti collected from brackish and fresh water habitats in Jaffna, Sri Lanka. Brackish water-derived Ae. aegypti were more tolerant of salinity than fresh water-derived Ae. aegypti and this difference was only partly reduced after their transfer to fresh water for up to five generations. Brackish water-derived Ae. aegypti did not significantly discriminate between 10 ppt salt brackish water and fresh water for oviposition, while fresh water-derived Ae. aegypti preferred fresh water. The hatching of eggs from both brackish and fresh water-derived Ae. aegypti was less efficient and the time taken for larvae to develop into pupae was prolonged in 10 ppt salt brackish water. Ae. aegypti isolated from coastal brackish water were less resistant to the organophosphate insecticide malathion than inland fresh water Ae. aegypti. Brackish and fresh water-derived Ae. aegypti however were able to mate and produce viable offspring in the laboratory. The results suggest that development in brackish water is characterised by pertinent biological changes, and that there is restricted genetic exchange between coastal brackish and inland fresh water Ae. aegypti isolates from sites 5 km apart. The findings highlight the need for monitoring Ae. aegypti developing in coastal brackish waters and extending vector control measures to their habitats.

Highlights

Aedes aegypti L. (Diptera: Culicidae) is the principal mosquito vector of yellow fever and, together with the closely related Aedes albopictus Skuse, a primary vector of dengue and chikungunya [1,2,3,4,5,6]
They show that brackish water-derived first instar Ae. aegypti larvae maintained at 10 ppt salinity demonstrated 100% survival to adulthood at salinities up to 12 ppt (Figure 2 B&D) while 100% survival in fresh water-derived Ae. aegypti maintained in fresh water was only observed up to 8 ppt salinity (Figure 2 A–D)
Some larvae from the brackish water colony maintained in 10 ppt salinity survived 20 ppt salt (Figure 2 D) while larvae from the fresh water colony maintained in fresh water could maximally tolerate only 16 ppt salt (Figure 2 C&D)

Summary

Introduction

Aedes aegypti L. (Diptera: Culicidae) is the principal mosquito vector of yellow fever and, together with the closely related Aedes albopictus Skuse, a primary vector of dengue and chikungunya [1,2,3,4,5,6]. (Diptera: Culicidae) is the principal mosquito vector of yellow fever and, together with the closely related Aedes albopictus Skuse, a primary vector of dengue and chikungunya [1,2,3,4,5,6]. Dengue is the most common arboviral disease of humans, with 50 million annual cases in more than 100 countries, an increasing incidence and global spread, and a 2.5% fatality rate in severe dengue [4,5]. Yellow fever has a zoonotic reservoir, is endemic to Africa and South America with the potential to spread to Asia and, an effective liveattenuated vaccine is available, responsible for 200,000 cases and 30,000 deaths in the world every year [6]. Dengue and chikungunya are endemic in Sri Lanka with a high incidence in the northern Jaffna peninsula [7,8]

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Conclusion