Switzerland expands measures to combat tiger mosquitoes

Switzerland recorded 2,639 mosquito reports in 2025, prompting the federal government to broaden its response to the Asian tiger mosquito. Bern is now assessing controls that target adult insects, alongside the larvicide programmes and breeding site inspections already used by cantonal authorities.

The new approach includes traps that combine carbon dioxide with other attractants to lure adult mosquitoes. Deployed across a sufficiently large area, the traps can reduce local populations. The government says researchers still need to establish how many traps are required, how they should be distributed and whether repeated captures produce a lasting effect.

The decision comes as the species continues to establish itself in parts of Switzerland. Geneva, Basel and Ticino are among the regions reporting the greatest activity. Zurich has also detected tiger mosquitoes in four neighbourhoods, according to a separate report published in April 2026.

The tiger mosquito is a public health concern because it can transmit diseases such as dengue and chikungunya when infected people introduce those viruses into areas where the insect is present. Switzerland has not adopted a single nationwide eradication model. Its response varies according to the mosquito's local spread and the appearance of imported disease cases.

The TIGER 2.0 project is testing whether carbon dioxide traps can work at Swiss scale. The Swiss Tropical and Public Health Institute is conducting the research with the University of Basel, focusing on the practical conditions that determine whether adult mosquito traps deliver meaningful local reductions.

Carbon dioxide mimics a signal produced by humans and other animals, helping attract adult mosquitoes. Additional attractants can make the devices more selective or effective. The government has acknowledged that large-scale deployment can work, while stressing that the evidence does not yet answer every operational question.

Researchers are examining trap density and placement, the long term effect of removing adult insects and the role of local socio-economic conditions. A neighbourhood's housing patterns, gardens, public spaces and capacity for regular maintenance could all affect the results.

That evidence will matter for municipalities considering whether to install traps in residential areas. A small number of devices may catch mosquitoes without significantly reducing the population. A dense network could be more effective, but would require funding, maintenance and coordination between federal, cantonal and local authorities. The government has therefore presented the adult control measures as trials that complement, rather than replace, existing work.

Sterile insect technique could cut local tiger mosquito populations by 60% to 70% when paired with conventional controls. The method releases sterile male mosquitoes that mate with females but produce no viable offspring. It targets reproduction rather than adult insects already flying through a neighbourhood.

Switzerland is investigating whether it can produce sterile males domestically. The programme could become operational in 2027 or 2028, although that timetable depends on research, production capacity and regulatory decisions. The government describes the technique as environmentally friendly, but also says it is significantly more complex and approximately three times more expensive than integrated vector control.

Sterile insect technique cannot stand alone. Authorities would still need to locate breeding sites, remove standing water and apply larvicides where appropriate. The stated reduction range applies when the sterile releases are carried out rigorously and combined with those traditional measures.

A related method, incompatible insect technique, releases males carrying a bacterium that prevents successful reproduction. The government sees greater potential in that approach in regions where mosquito-borne diseases are widespread. In Switzerland, however, the bacterium already exists in tiger mosquitoes, at least in Ticino. Local populations may therefore have developed resistance, while the ecological effects remain difficult to assess.

Of 2,537 valid mosquito reports in 2025, 774 involved tiger mosquitoes. That represented 31% of valid reports, according to figures cited by the federal government. The numbers show both the scale of public reporting and the importance of verification by specialists.

Authorities are using a phased system to decide how aggressively to respond. In cantons where tiger mosquitoes have not appeared, or where sightings remain isolated, the priority is rapid eradication of breeding sites. Small containers, plant saucers, blocked drains and other pockets of standing water can provide the conditions needed for larvae to develop.

In areas where the species is well established, classified as phase two, the focus shifts to sustained vector control. Larvicides are a central tool because they target immature mosquitoes before they emerge as adults. Phase three applies where imported cases of disease have been detected. There, authorities are expected to intensify control around potential transmission areas.

This system gives cantons room to match measures to local conditions. It also requires residents, municipalities and health officials to act on reports quickly. Geneva, Basel and Ticino face a heavier operational burden than cantons with occasional detections, while Zurich's recent sightings show that the geographic picture can change from year to year.

The federal government has accepted the need for more tools, while withholding support for every proposed technology. It responded to a postulate from parliamentarian Sarah Wyss, who called for newly appearing invasive species to be tackled rigorously and for federal backing of projects based on current scientific evidence.

Bern says the responsibilities raised in the postulate have already been addressed through existing programmes and the new assessment of complementary techniques. The position leaves implementation largely dependent on evidence from ongoing trials, including TIGER 2.0 and the Swiss investigation into sterile male production.

For residents, the immediate response remains familiar: remove standing water, report suspected tiger mosquitoes and follow cantonal instructions. Municipal services must continue inspecting breeding sites and applying larvicides where the phased strategy calls for them. Traps and reproductive control could add capacity, but neither has yet been approved as a universal replacement for integrated vector control.

Switzerland's next decisions will depend on results that are still being collected. Researchers must show how adult traps perform across different neighbourhoods, whether sterile releases can be produced reliably and how much each intervention costs. The government will then have to determine where new measures offer a clear benefit over the controls already in place.