High Salinity Tolerance of Aede s to Breed in Brackish Waters Around the Negombo Estuary

Abstract

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In the midst o f dengue control programs, a high occurrence o f dengue and dengue hemorrhagic fever cases around the Negom bo estuary is reported at the Centre for Clinical Management o f Dengue & Dengue Haemorrhagic Fever, Negom bo, during April/May and Sept/Oct 2014. Although preimaginal development o f ylecfes-dengue vector mosquito is known to exist in fresh water environment for many years, few recent findings have revealed the possibility o f A edes breeding and immature stage development in brackish water conditions. In Negom bo estuarybeing a partially enclosed coastal body o f brackish water, w e investigated the possible A edes mosquito breeding in brackish water in and around the lagoon. Natural breeding sources were examined, and an ovitrap based study was also carried out to investigate the possible breeding, immature stage development, hatching and adult emergence in brackish water environment. The study revealed the oviposition preference (0-22 ppt), egg hatching (0-6 ppt in field conditions and 0-6 ppt in laboratory conditions for Ae.aegyptr, 0-14 ppt in field conditions and 0-18 ppt in laboratory conditions for Ae. albopictus) and preimaginal development (0-6 ppt in field conditions and 0-6 ppt in laboratory conditions for Ae.aegyptr, 0-14 ppt in field conditions and 0-14 ppt in laboratory conditions for A e.albopictus) o f A edes mosquitoes. Further, the study reported the natural prevalence o f preimaginal stages o f Ae.albopictus in brackish water collections (2-14 ppt) around the estuary. The study confirmed the brackish water breeding o f A edes m osquitoes around the Negom bo estuary. Higher salinity tolerance, compared to brackish water collections o f the Northern coast, Sri Lanka was revealed. Negom bo, being a fishing village and having a high population density, the study identifies the potential risk o f dengue transmission in the area by providing breeding grounds for vector mosquitoes and possibly explains the high occurrence o f dengue incidence around the lagoon. Further, the study suggests incorporating larvivorus fish and removing trapped receptacles in the marshy environments to intensify the control programs.