Tiger mosquitoes on France’s Reunion Island are being driven back by a new method that releases sterilised males into the wild – a technique scientists say could halt epidemics of diseases spread by the insects’ bites, including dengue and chikungunya.
Issued on:
3 min Reading time
Mosquito populations have fallen by around 40 percent in targeted areas within a year, after researchers released sterilised male mosquitoes that mate with females whose eggs never hatch.
The method was developed by researchers from CIRAD, a French agricultural research centre, and IRD, a French research institute, which have been working on mosquito control on the island for years.
Every week, hundreds of thousands of these tiger mosquitoes are bred at the IRD insectarium, put to sleep and sent to CIRAD laboratories, where they are sterilised using X-rays.
“There are a lot of them – 193,000 Aedes albopictus, or tiger mosquitoes,” Mathieu Whiteside, a medical biology technician at IRD, told RFI.
Once sterilised, the insects are taken to Saint-Joseph in the south of the island. There, they are released in an experimental zone where 74 percent of the population sampled has already contracted dengue or chikungunya.
Releases have taken place there every week since August 2025, both on the ground and by drone.
“These drones allow us to reach areas we couldn’t access by land,” explained Jérémy Bouyer, research director at CIRAD and coordinator of the joint project, known as Optis.
Bouyer himself has developed a device that releases the mosquitoes in a steady, controlled flow throughout the flight.
France sees record spike in chikungunya cases as tiger mosquito spreads
Stopping the spread
The method relies on releasing only male mosquitoes, which do not bite humans.
“The idea is to breed them, keep only the males, sterilise them and release them into the wild,” said Cécile Brengues, IRD coordinator for the Optis project.
“The males go and mate with wild females, and the wild females lay eggs that never hatch.”
Researchers have gone a step further by adding a larvicide, pyriproxyfen, which is applied to the males after sterilisation and carried back to breeding sites.
“With the classic insect sterilisation technique, you induce sterility, but if you stop, the mosquito population recovers in three or four weeks,” Bouyer explained. “Here, because we also treat the breeding sites, the effect lasts for several months.”
If the method is used at the right point in the mosquito season – for just three or four months a year – Bouyer said it could block epidemics for the whole year.
Early results are promising. Releases carried out since August 2025 across 60 hectares have cut mosquito populations by between 35 and 55 percent, depending on the area.
Macron promises vaccines as chikungunya kills baby on Reunion Island
Scaling up
Research on this method began on Reunion in 2009, ahead of similar programmes in Singapore.
Since March, the project has expanded to 175 hectares, with a goal of cutting tiger mosquito numbers by 80 percent within a year. Studies so far show no impact on other species.
“We are in the phase of maximum surface control, but we still need to carry out a serological survey at the end of the 12 months of releases to measure the impact on transmission,” Bouyer said.
In the study zone where the programme is being tested, 63 percent of people sampled had contracted chikungunya, either during the 2005-2006 epidemic or the 2024-2025 outbreak, while 11 percent had contracted dengue.
Those figures underline how exposed the area is, as researchers now look to scale up the technique.
The next step is to expand the programme by handing it over to a start-up, which plans to build a sterile male production facility in Saint-Joseph and automate releases, including through artificial intelligence.
Residents still need to protect themselves and help eliminate large breeding sites such as abandoned pools or vehicles, which are harder to control.
Cost also remains a key question. Control via sterilisation is estimated at €500 per hectare per year in the areas most affected by epidemics. For now, Optis is funded by the Reunion regional authority and the European Union’s regional development fund.
This story was adpated from the original version in French and lightly edited for clarity.
