How did the insect, identified in 67 departments, colonize France?

It goes north. Gain territory. Every year a little more. Already widely present in France, Aedes albopictus, better known as the tiger mosquito, continues its colonization: 67 departments have been placed on red alert by the Vigilance mosquitoes site, three more than last year.

How to explain the progression of the tiger mosquito in France? Should we be worried about it?

An expanding colonization

Meurthe-et-Moselle, Val-d’Oise and Loiret are the three additional departments where “the tiger mosquito has been declared officially implanted and active”, indicates Vigilance moustiques, confirming the data from the map published by the Ministry of Health. In total, “nearly 70% of metropolitan departments are affected by colonization, adds the monitoring platform. It therefore continues its ascent of the country with nearly two thirds of the south almost entirely colonized”. However, “its presence is not the same throughout the territory: while the departments in red vigilance of the northern half are considered as weakly colonized (less than 40% of the population is concerned), the southern third is now almost entirely affected”, observes Vigilance mosquitoes.

“From the moment the tiger mosquito has been detected in a department, it is placed on alert (yellow, orange or red depending on the extent of its presence), explains to 20 minutes Anna-Bella Failloux, entomologist specializing in the tiger mosquito at the Institut Pasteur. But that does not mean that the densities are as high there as in the most affected areas such as Montpellier or Nice, where it has really become a pest. Over there, we get bitten repeatedly as soon as we are outside, including during the day, unlike the classic mosquito – the culex – which only bites after dark. In the new departments where it has been identified, we have not reached this stage”.

Climate change (and us) in question

But how to explain the progression of this insect previously present in overseas territories? “Climate change, associated with globalization, urbanization and deforestation, contributes to the increase in the transmission of vector-borne diseases, in particular transmitted by the Aedes albopictus mosquito, which has been spreading for several years in Europe and France”, recalls Public Health France.

“The tiger mosquito has been in France since 2004. And since then, it has gradually colonized the metropolis, department by department, whereas at the start it was very little present, recalls Anna-Bella Failloux. He has learned to adapt to the environment he is colonizing, in which he has no real competition”. And “if it has spread so much in France, it is because it is very much linked to human activities, explains the entomologist. Due to its biology, it is qualified as an invasive species: it lays eggs capable of withstanding extreme conditions, both cold and drought. Several months after laying, whether the egg has remained at very low temperatures or has been dried up by weeks of high heat, as soon as there is a little water, it will turn into a larva of mosquito. Characteristics that allow it to travel in the form of eggs, whether with plants, when moving, under tires. Without forgetting all the water reservoirs – pots, watering cans and other saucers – in our gardens, which constitute a large part of the breeding sites, these environments where mosquitoes will come to lay eggs and proliferate. All this means that we largely participate in the dissemination of this mosquito without knowing it”.

A cocktail of climatic and human factors that promotes its colonization. “Increasingly, the weather is nice earlier in the year and cold later, with a tiger mosquito season which generally extends from May to November in the more northern regions, details Anna-Bella Failloux. But in the South, it is present almost all year round”.

A virus-carrying mosquito

However, the tiger mosquito “can transmit the Dengue, Chikungunya and Zika viruses”, underlines Public Health France. So should we be worried about its progression and fear viral epidemics? “In metropolitan France, you have to put things into perspective. In our latitudes, there are not so many fears to have compared to the situation of the tiger mosquito in the overseas territories, reassures the entomologist. In France, the situation is simple: these viruses do not exist in situ, they must be imported. After more than two years of the Covid-19 pandemic, with the resumption of the movement of people, we can expect imports of the virus by people returning from areas where they circulate naturally. Some will be bitten there and, for some of them, be infected. If, on returning to mainland France, these people are again bitten by a tiger mosquito, the virus will replicate in him (or rather her, because it is the female who bites). After a few days, by biting another person, the mosquito will inject the virus contained in its saliva”.

“This may have caused autochthonous cases of Dengue, Zika and Chikungunya in France, which proves that the tiger mosquito is a vector of transmission, insists Anna-Bella Failloux. But this only gives rise to isolated cases: the maximum we have observed is a dozen cases of Chikungunya in Montpellier in 2014. On the other hand, there was an epidemic in Italy in 2017, with more of 300 cases of this virus identified in the Rome region. So transmission is possible. But because we have a very efficient surveillance system thanks to sentinel doctors and mosquito control operators, we manage to cut off transmission from the start and prevent the occurrence of epidemics”.

Provided also that individuals play their part. However, “it is not always easy to spot it. But since the viral epidemics in the Overseas Territories, people have become more aware: they know that when a mosquito has black and white striped legs, it is most certainly a tiger mosquito, and that it can transmit diseases. , summarizes the entomologist. On the other hand, making the link between this biting mosquito and the breeding sites that we create in spite of ourselves is more complicated. If we do not generate them or if we eliminate them, we avoid its presence. So we must not be alarmist, but be careful not to encourage its proliferation”.