INTERVIEW - "So far, we have been able to prevent the transmission of diseases," says the researcher who releases sterile tiger mosquitoes in Ticino

Anyone traveling in Ticino in the summer will likely encounter not only lizards and alpine choughs, but also a far more exotic creature: the Asian tiger mosquito. This insect, which can transmit tropical diseases, has established itself in large parts of southern Switzerland. Biologist Eleonora Flacio first identified the tiger mosquito in Ticino in 2003. As head of the Vector Ecology Department at the Ticino University of Applied Sciences (SUPSI), she has been fighting the invasive mosquito ever since.

Ms. Flacio, why is it important to keep the tiger mosquito in check?

First of all, the tiger mosquito is very annoying because it bites during the day, often several times in a row. This can make a visit to the park or reading in the garden very unpleasant. It is also a potential carrier of tropical diseases such as dengue, Zika, or chikungunya if it has previously bitten an infected person.

The World Health Organization warned just this week that the Chikungunya virus is currently spreading rapidly worldwide. Have any of the diseases you mentioned been transmitted in Switzerland yet?

No, but there are recurring local outbreaks in France, Italy, and Spain. In Switzerland, there have only been cases of the disease so far in which people became infected abroad. We have been able to prevent subsequent transmission by mosquitoes. This is also thanks to our rapid response system.

How does the system work?

Our research group monitors tiger mosquitoes in Ticino. We know exactly where and how many there are. If someone returns from vacation with one of these tropical diseases, the cantonal doctor contacts us. If there is a risk of transmission because the mosquito density is high where the infected person lives, we notify the municipality. Within a 100-meter radius of the home, the breeding sites and adult tiger mosquitoes are then targeted with active ingredients.

How often do you have to carry out such missions?

Last year, there were five cases, and three were treated. The critical period is between July and September, when many people travel and mosquito density is at its highest.

The tiger mosquito originates from Southeast Asia. How did it get to Ticino?

In the 1990s, mosquitoes traveled from China to Italy via the USA. This occurred through the trade of old car tires, which had accumulated water. From Italy, they spread along the traffic routes, as stowaways in cars. I detected the first mosquitoes in Ticino in 2003.

Have you discovered the first tiger mosquito in Switzerland?

Yes, at a rest stop on the A2, she laid her eggs in one of my traps. These are black cups with a little water and a piece of wood inside. Tiger mosquitoes like small pools of water in the dark as breeding grounds. This makes them easy to detect. Back then, I was still fighting mosquitoes alone as a scientist; today, I lead an entire team.

How do you combat mosquitoes?

We work closely with the municipalities. They help us with monitoring by regularly replacing the cup traps mentioned. Where mosquitoes are prevalent, workers apply grains containing BTI. This is a biological agent that only harms mosquito larvae but is harmless to humans and the environment. The municipalities also inform the population. This is important because 80 percent of breeding sites are located on private property.

What can the public do against tiger mosquitoes?

The first step is to avoid potential breeding grounds. Containers in the garden or on the balcony should be emptied regularly. Water that has been standing for more than a week is ideal for egg-laying. Even a single flowerpot saucer is sufficient. Where the water cannot be removed, you should spread BTI once a week. The seeds are very easy to apply. It's a bit like adding salt to pasta water.

How effective is the Ticino system?

Very effective. Compared to Italian areas where there is no consistent control, we were able to reduce the tiger mosquito population by 74 percent. The tiger mosquito density in Ticino has been stable for over five years.

Now your research group is testing a new method: releasing sterile male mosquitoes. How does it work?

These are male tiger mosquitoes that have been treated with X-rays. Their DNA is damaged, making them infertile. We release these males. After they mate with females, the females lay eggs that do not hatch into larvae.

Despite damaged DNA, are these males still fit enough to mate?

They are, in fact, not as lively as healthy males. We have to release about ten times more mosquitoes than there are in the area to effectively displace the resident males. If a female had the choice, she would never engage with one of our males.

Where have you already released the mosquitoes?

Over the past two years, we have tested the method in an isolated area on Lake Lugano. We have demonstrated that it works and complements existing measures well: mosquito numbers have been reduced by 63 percent.

How can the method be used optimally?

It seems realistic to us to use sterile mosquitoes to protect very specific locations, such as a school, a hospital, or a tourist hotspot. That's why we're conducting trials in smaller areas this year. We originally planned 21 locations, but the Swiss National Science Foundation rejected our application because the research was too applied. Now we're limited to two locations: a residential area in Ascona and a hotel complex in Losone.

Can you already report on initial results?

In Ascona, the effect isn't yet visible. But in Losone, the number of mosquitoes has already decreased. The hotel owners told us they haven't seen any mosquitoes this year.

How expensive is a deployment with sterile mosquitoes?

A sterile male costs about two cents. For an area of 12 hectares, such as the one in Losone, we release approximately 36,000 sterile males per week. The cost is approximately 720 Swiss francs per week and 18,000 Swiss francs for the entire summer. The municipality of Ascona and the hotel pay for the mosquitoes, and we, as a research institute, finance the scientific monitoring.

Isn't the method far too expensive to be used on a large scale?

It's still too expensive for that. We source the sterile mosquitoes from a company in Bologna. But in the future, we'd like to breed sterilized mosquitoes ourselves in Ticino to minimize costs. This would lower our unit price, and we'd have to release fewer animals, as the Ticino mosquitoes would be fitter and not weakened by the long journey. We could then supply the rest of Switzerland with these mosquitoes.

Where has the tiger mosquito already established itself in Switzerland?

It was first detected north of the Alps in 2013. Stable populations already exist in Basel, Geneva, Valais, and small parts of Bern and Zurich. The tiger mosquito is expected to spread even further in the coming years. Once established, it's impossible to get rid of it. The challenge then is to keep the animals under control.

Many people confuse the tiger mosquito with other species. How do you identify it?

The tiger mosquito is black with white stripes on its legs and body, with the white line on its back being particularly distinctive. It is often confused with the Asian bush mosquito, which has established itself throughout Switzerland. The bush mosquito is also black with white stripes. However, it is larger and lacks the white dorsal line. Anyone who suspects they have spotted a tiger mosquito can send a photo to the Swiss Mosquito Network . Experts there will help identify the animal.

How do you protect yourself from the bites of the tiger mosquito once it is there?

It's recommended to spray yourself with mosquito repellent. It's best to do this several times a day, as sweat dilutes the repellent. White clothing, mosquito nets, and screens on windows also help. However, the new trend of placing automatic insecticide sprayers in your garden is truly unfortunate. These devices also kill beneficial insects, are harmful to humans, and can promote resistance in tiger mosquitoes. This makes our work more difficult.

How can we in Switzerland improve our approach to dealing with the tiger mosquito?

While Ticino is playing a pioneering role, each canton must find its own way of dealing with the tiger mosquito. Public awareness is also crucial. Everyone can do something to minimize the number of breeding sites. People shouldn't expect the authorities to do everything for them; they should take action themselves. In Ticino, this is already working quite well.