Millions of sterile male tiger mosquitoes are being released across France in an attempt to reduce their numbers, with a trial by Montpellier-based company Terratis now entering its second year.
The first releases took place in spring and summer 2025 in Brive-la-Gaillarde, and releases have since also been carried out in Montpellier, Toulouse and areas near Lyon.
The technique involves flooding local mosquito populations with sterile males. Females mate with these males but then produce unfertilised eggs that do not hatch. A key advantage is that male mosquitoes do not bite.
Clelia Oliva (centre) with colleagues at a sterile mosquito release in MontpellierTerratis
The approach, known as the sterile insect technique, has been used as an eco-friendly way of controlling insect pests for decades, but has not previously been widely deployed against tiger mosquitoes.
Terratis specialises in developing technologies to breed sterile insects on a large scale, including improved methods for separating male and female mosquitoes — a crucial step because only males are released.
“Our ambition is to grow, industrialise and have a real impact, helping to greatly reduce mosquito numbers in France,” said Clelia Oliva, co-founder and chief executive of Terratis.
Tests carried out at the end of 2025 showed a reduction in mosquito breeding in Brive following initial trials. Earlier limited trials in parts of Réunion reported reductions of 50%-60% in mosquito populations within a year.
Female mosquitoes mate only once and feed on animal blood to obtain the protein needed to produce eggs. They can lay around 300 eggs, which usually develop within five to 10 days.
Males, by contrast, mate with multiple females and feed only on nectar and fruit.
Tiger mosquitoes tend to remain close to where they were born, meaning that releasing sterile males in targeted locations can have a significant local effect. Potential areas for releases include parks, gardens, public squares, airports and cemeteries.
A second trial began in Montpellier in 2025, while areas around Lyon and Toulouse have since been targeted.
As an invasive non-native species, reducing their numbers is not expected to cause ecological harm.
“The principle is simple: you raise mosquitoes in captivity, separate males from females, sterilise the males with X-rays and then release lots of them,” said Dr Oliva. “But it requires enormous technical expertise.”
Terratis has established a 200m² facility where mosquitoes are raised throughout the year. Several tasks, including collecting eggs, still have to be carried out manually.
“Automation is the most important thing. The first step was to robotise larvae production. It allowed us to raise more and to improve working conditions,” Dr Oliva said.
placing sand in flower pots and saucers to prevent water collecting;
removing containers where water can gather;
using mosquito traps where appropriate.
Tiger mosquito sightings can be reported via the Agence nationale de sécurité sanitaire de l'alimentation, de l'environnement et du travail (Anses) website.
