Pre-imaginal development of Aedes aegypti in drains containing polluted water in urban cities in Sri Lanka

Dengue control in Sri Lanka targets the removal or treatment of fresh water bearing containers that provide breeding sites for Ae. aegypti. Health authorities have raised concern that the incidence level of dengue remains high in urban settings due to ignorance of dengue mosquito larval surveillance on polluted water drains. The present study was designed to evaluate the presence of Ae. aegypti in the polluted water drains in some urban areas in the country. A preliminary entomological survey was carried out in urban areas from Chilaw to Galle and further studies were carried out in the drains with polluted water that marked the presence of Ae. aegypti larvae. Presence of Ae. aegypti was recorded in drains containing polluted water in Galle city for the first time in Sri Lanka. The most commonly observed species in the preliminary survey was Cx. quinquefasciatus (97.5%) followed by Cx. gelidus (0.99%), Ae. albopictus (0.62%) and Ae. aegypti (0.42%). Water quality characteristics revealed low dissolved oxygen and high conductivity with visible organic pollutants. Constant insecticide pressure and the destruction of the breeding sites through source reduction in vector control campaigns compel the mosquito to adapt to new ecological niches. Therefore, appropriate surveillance and control measures should be implemented by health authorities to control vector mosquitoes and lower the disease burden.