As Bangladesh’s cities grow brighter after sunset, researchers are confronting an unsettling change in the behaviour of the mosquito responsible for spreading dengue: Aedes is no longer necessarily calling it a day when darkness falls.
Aedes mosquitoes, traditionally considered predominantly daytime biters, are increasingly being observed active after sunset in Bangladesh.
Laboratory and field research abroad has also found that artificial light at night can increase or prolong mosquito activity.
The findings raise a question with potentially important implications for Bangladesh’s dengue control strategy: could increasingly illuminated urban nights be extending the hours in which people are exposed to Aedes bites?
There is no direct evidence yet that Dhaka’s LED streetlights or other artificial lighting are increasing dengue transmission.
Researchers caution that establishing such a link would require Bangladesh-specific studies comparing mosquito behaviour under different lighting conditions.
But the question has assumed greater urgency as Bangladesh faces another severe dengue season, with transmission spreading well beyond Dhaka.
Aedes active after sunset
Professor Kabirul Bashar, a zoologist at Jahangirnagar University who has extensively studied Aedes mosquitoes, said their nighttime activity can no longer be ignored.
“The density of Aedes mosquitoes is slightly lower at night. However, Aedes mosquitoes still bite during nighttime,” he told Dhaka Tribune.
“Previously, these mosquitoes used to bite only during the day, specifically in the morning and afternoon.”
Research conducted by Bashar and colleagues between 2021 and 2023 collected 134,904 mosquitoes from Jahangirnagar University, Savar, Chittagong and Cox’s Bazar.
Monitoring between 4pm and 9pm found Aedes mosquitoes remaining active into the evening, including around 9pm.
The study establishes that Aedes can remain active after sunset in Bangladesh, but it did not compare areas according to artificial-light exposure.
It therefore cannot establish whether brighter nights are responsible.
Dhaka’s nights getting brighter
What is clear is that Dhaka’s nighttime environment has changed dramatically.
A 2026 study published in Environmental Sciences Europe, using VIIRS satellite observations from 2014 to 2023, documented a substantial expansion of artificial nighttime illumination in Dhaka, with researchers estimating an annual increase of 7.2%.
Some of the brightest concentrations were around the airport, Gulshan, Banani, Dhanmondi, Motijheel and Tejgaon.
Across Dhaka and other major cities, older streetlights have increasingly given way to brighter white LED systems, while commercial areas, buildings and public spaces remain illuminated for longer.
The satellite findings establish the expansion of nighttime light, not a connection with dengue.
What artificial light may do
International research, however, offers a possible biological mechanism.
A 2020 laboratory experiment found 82% of female Aedes aegypti fed during daytime under normal experimental conditions, compared with 29% at night.
After a 30-minute exposure to white light, nighttime feeding increased to 59%.
A 2025 US field study of Aedes albopictus at 58 locations similarly found greater nighttime activity at sites experiencing higher artificial-light pollution, particularly following very hot days.
Neither finding can be directly extrapolated to Bangladesh because mosquito species, climate and real-world lighting conditions differ.
Professor Humayun Reza Khan of Dhaka University’s Zoology Department said those limitations make local research essential.
“Artificial light at night can affect animal behaviour, but the nature and extent of that effect can vary from one species to another,” he said.
“We cannot say exactly how light pollution is affecting a particular animal or mosquito species without conducting specific research.”
For Bangladesh, that would mean comparing Aedes activity in otherwise similar neighbourhoods with different levels and types of illumination, while measuring brightness, wavelength, colour temperature, duration and nighttime temperatures.
Until such research is conducted, brighter streets cannot be blamed for Bangladesh’s dengue surge.
But as cities remain awake, and illuminated, for longer, scientists say an old assumption underlying dengue prevention may warrant reconsideration: that the mosquito biting people during the day rests when night falls.