200,000 sterile tiger mosquitoes released in Toulouse
City latest to adopt experimental technique for curbing numbers of disease-carrying mosquitoes
Male mosquitoes do not bite, as they feed primarily on flower nectar and other sugary sources
Alan Mirza/Shutterstock.
Multiple communes have begun releasing sterile male tiger mosquitoes in an effort to reduce their populations, with Toulouse the latest city to join the scheme.
On May 26, 200,000 sterile male tiger mosquitoes were released in the city centre after residents complained of worsening infestations, particularly in neighbourhoods near a central Toulouse cemetery.
The mairie said recent warm temperatures and rainfall had accelerated mosquito proliferation in the area.
Before the decision was taken by the Toulouse city council, residents had reported an escalating mosquito problem, with one woman telling RMC: “We’re completely infested. We can’t keep the windows open any more. There is nothing we can do.”
As a result, the municipality launched a trial using sterile insect technique. Officials said the method was chosen as an alternative to chemical treatments and is being carried out without pesticides or insecticides.
The method works by releasing sterile male mosquitoes that mate with females, resulting in empty eggs and a gradual reduction in the population. Male mosquitoes do not bite, as they feed primarily on flower nectar and other sugary sources, meaning their release does not contribute to the problem.
The Toulouse trial follows a successful initial experiment in Brive-la-Gaillarde, Corrèze, in 2025, during which eleven million sterile mosquitoes were released in phases at a rate of around 400,000 per week. The city later reported a reduction in mosquito nuisance levels, with results described as encouraging, and the Brive project is now serving as a reference for other municipalities.
Clélia Oliva, co-founder and president of Terratis, the start-up behind the initiative, said that the approach “had achieved up to 50% efficiency in the protected area”. She added that sterile males disperse through targeted zones and mate with wild females that are “very present on the site”, preventing them from producing viable eggs.
Following the trial, Montpellier in Hérault and the commune of Mions in the Lyon metropolitan area also adopted the approach, with Toulouse being the latest city to deploy Terratis’ services.
The method is considered a complementary tool alongside traditional mosquito control measures, rather than a standalone solution.
Residents can also take simple preventive measures to reduce mosquito bites and limit breeding sites. Health authorities advise removing any stagnant water around homes and gardens, using repellents and mosquito nets, wearing long, loose-fitting clothing, and regularly emptying containers such as plant pots, buckets and pet water bowls.
Travellers are also urged to take extra precautions in affected regions and to remain vigilant for several weeks after returning.
First detected in France in 2004, tiger mosquitoes can spread serious diseases including dengue fever, chikungunya, and zika virus.
There have been numerous ‘native’ cases of dengue and chikungunya in mainland France in recent years, meaning that the patients had become infected on French soil.
Last year, a record number of native cases of chikungunya were recorded following several outbreaks.
