Faulty drainage and waste management systems along with poor monitoring from the authorities concerned are among the major causes of the high density of Culex mosquitoes in Dhaka that puts the urban health at risk.
The density of Aedes mosquitoes is on the decline, mainly due to the temperature drop in the winter. The Aedes mosquitoes would return with the temperature rise and monsoon rains, they added.
This situation makes the mosquito menace a permanent problem for the city, putting its urban management system and administrative capacity in question.
Prof. Kabirul Bashar, a medical entomologist and teacher of Jahangirnagar University, told the FE that the high density of Culex mosquitoes would be at peak in March. The density would reduce from then with rise in temperature, and start of monsoon rains and nor'wester in April.
It would take two more months for the return of dengue, as Aedes mosquitoes are attacked by dengue virus in 6-8 weeks, starting from June, he added.
Data from the last week of December 2025 showed that about 85 per cent of the total adult mosquito samples collected in Dhaka were of Culex species, noted one of his recent surveys.
Besides, unplanned drainage system, drains that were not cleaned for years, waterlogged basements, and parking areas turned Dhaka into an ideal breeding ground for Culex mosquitoes.
"Poor regulation, and faulty drainage and waste management system are among the main causes responsible for the uncontrolled growth of Culex mosquitoes. The authorities need to keep the city's drains clean ," he said.
Culex mosquitoes have long been neglected due to the misconception that they 'do not spread diseases'. However, these mosquitoes are carriers of filariasis, and most importantly, they make people's daily life unbearable.
"However, we haven't recorded any Culex mosquito-caused filariasis in the city."
According to the mosquito surveillance data of Jahangirnagar University, the density of Aedes mosquitoes and the Bretto Index have decreased, which is undoubtedly positive. But this decrease is not a permanent success; it is just a temporary break, according to the expert.
All the factors for Aedes breeding are still present across the city - in the alleys, roofs, under-construction buildings, water tanks, plastic drums and buckets. Aedes can spread its wings again when the monsoon arrives.
Structural renovation of drainage system, mandatory provision to prevent water from accumulating in basements and parking areas, environment-friendly larval control in lakes, canals and water bodies, and special programmes identifying slums and waterlogged areas as 'high-risk zones' can help improve the situation.
"It is impossible to make Dhaka mosquito-free without the citizens' active participation," he added.
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