French authorities to release millions of sterile tiger mosquitoes

Several local authorities in France are releasing millions of tiger mosquitoes into the wild, in a bid to reduce overall numbers. The secret? The mosquitoes are all sterilised males.

Flooding the environment with sterilised male insects is a measure that has already been successfully tested in other countries with tiger mosquitoes present including Singapore and Hong Kong, as well as with other forms of invasive species such as screwworm in North and Central America.

A similar scheme took place in Brive-La-Gaillarde, Corrèze in 2025 with millions of sterile tiger mosquitoes released, and another has been underway in French overseas region Réunion since August 2025.

The measure stems from the insects’ inability to reproduce, and eventually reduces the number of tiger mosquitoes in the local area.

Sterile start-up scaling

The process, dubbed TIS (‘technique de l'insecte stérile’), is being implemented by Terratis, a Montpellier-based biotechnology start-up.

Terratis founder Clélia Oliva explained that the company is now working to industrialise the technique. 

“This year, we have considerably increased our production capacity to a million and half [sterilised] males per week.” The process does not use pesticides, and is respectful to the environment, to health, and to biodiversity, she told France 3.

“In the short-term, we are planning to develop our first massive-scale ‘factory’. This will allow us to respond to high demand, particularly from commune authorities,” she said.

The male mosquitoes are raised in stagnant water tanks, sterilised using X-rays, and then released, either at ground level or overhead using drones. Female insects will still mate with the males, though as the latter are sterile, eggs will not be fertilised and new insects will not hatch. The net result is a significant drop in new insects.

The short lifespan of tiger mosquitoes – around 21 days – means that females will be unlikely to find a non-sterile mating partner after first attempts to mate with a sterile male.

As mosquitoes tend to remain in the same location throughout their lives, rarely flying more than a kilometre from where they hatch, the plan can significantly reduce numbers within a concentrated area.

Tiger mosquitoes are now present across all mainland French regions following the first confirmed sighting in 2004.

The planned influx of mosquitoes will not have any negative consequences for humans, as male mosquitoes do not bite – only females do so when seeking blood for egg production.

Major commune investment

The commune of Mions, in the Métropole de Lyon (Auvergne-Rhône-Alpes), will see almost 200,000 sterilised males released in blocks over the spring and summer, as part of a €60,000-plus investment in the project.

It is hoped that the summer tiger mosquito population will reduce by 50% compared to what it would be without releasing sterile males.

The eventual plan is to release five million sterilised male mosquitoes each year nationwide, cutting the population by 50% in the first year and up to 90% from the second year onwards.

“We put more than 3,000 insects in the [X-ray] box at a time,” said Florian Vernichon, specialist in Mions, to Sud Ouest. “[The males] lose the ability to fertilise the females.”

Mions is the third commune to implement the sterilisation system with Terratis after Brive-La-Gaillarde and Montpellier (Hérault).

The commune chose to fund the sterilisation project after concluding that existing traps were ineffective and not worth the cost. 

“Helping people to buy anti-mosquito traps doesn’t necessarily work,” said Mickaël Paccaud, Mions mayor, to France 3. “We must look at the evidence, and we must do something that works, because we are talking about public health above all.”

This being said, residents in regions where sterilisation programmes are taking place are still encouraged to engage in best practices to reduce the risk of tiger mosquitoes, including clearing stagnant water from their land.

Spreading diseases

Tiger mosquitoes were first detected in France in 2004, and in this particular commune in 2013. They 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, and had not recently travelled to an ‘at-risk’ country. In 2025, record native cases of chikungunya were recorded following several outbreaks.

In a press release from April 23, regional health agency l’Agence Régionale de Santé said: “In Auvergne-Rhône-Alpes, 2025 was marked by a high number of [mosquito-spread] cases and a steady increase in the tiger mosquito population across all departments. 

“With the surveillance period for these diseases beginning on May 1, the ARS and Santé publique France are reviewing the situation in 2025, and reminding the public of the essential measures to limit its spread.”