The insect, which was previously an unavoidable surprise guest of summer holidays, is now visible until December in some regions. An entomologist explains the causes and consequences of this phenomenon to franceinfo.
At the beginning of November, mosquitoes, usually confined to the summer period, continue to attack us, day and night. How to explain it and what are the consequences? Frédéric Simard, research director at the Research Institute for Development in Montpellier, sheds some light on the question.
franceinfo: Mosquitoes bite us later and later in the year. Is it just a feeling?
Frédéric Simard : It's not just an impression, there are still mosquitoes at the end of October! Last year, we captured the tiger mosquito until December in the Occitanie region. Mosquitoes are no longer confined to summer, because summer is extending, a consequence of climate change. The temperatures are still very mild, there has been abundant rainfall. Flooded cellars are, for example, excellent breeding grounds for the common mosquito, the culex.
“So there is water and heat, it is optimal for the development of mosquitoes.”
Frédéric Simardat franceinfo
And this is likely to last as long as we do not have a drop in temperature, with frosts. We see that the period of reinforced surveillance of the tiger mosquito extends from May 1 to November 30, but we realize that this is no longer sufficient. We begin to see larvae developing, or even adults, from April.
What are their strategies for getting through the winter?
The eggs of the tiger mosquito will not hatch in winter, as this is essentially determined by the length of day versus night, the photoperiod. So currently, fewer and fewer eggs are hatching. But females born a few days ago have a significant longevity, because the conditions are ideal. It is especially these which continue to bother us, while mosquito production itself decreases with the approach of winter. The culex will spend the winter as an adult, and will go into cellars or caves and will stop all activity, in a state of hibernation. And at the beginning of spring, they will come out to lay eggs and create a new generation.
Can artificial light disrupt this winter break?
It's a research question. When there is artificial light, the tiger mosquito, which bites during the day, will bite late at night. Light pollution can have an impact on the entire biology of these mosquitoes in urban areas, but it is too early to give results.
How to get rid of these mosquitoes?
It is only with temperatures below ten degrees that we will get rid of mosquitoes which are currently adults. But the eggs of tiger mosquitoes are insensitive to external variations, they are resistant to frost. They are placed in the environment, and only wait for spring to hatch. These are little time bombs that we have everywhere in our gardens, in our flowerpot cups. The fact that they fill and dry out regularly favors the installation of these eggs. You must therefore empty your cups, especially in spring, it will be very important to do so. Autumn is a good time to clean up the garden, or the balcony, or to remove cat bowls from dogs that are lying around.
“We should not expect everything from public authorities, since according to the figures, the tiger mosquito is mainly produced in private spaces, and not in public spaces.”
Frédéric Simardat franceinfo
It is everyone's responsibility to avoid producing mosquitoes which must then be eliminated with insecticides.
What is the impact of this increased mosquito activity?
The tiger mosquito can transmit dengue, chikungunya and Zika viruses. For the culex, it is West Nile or Usutu. The fact that the period of mosquito activity is extending further increases the risk of transmission of these viruses which are imported every day into mainland France by travelers from tropical areas where epidemics are rampant. There is constant pressure. As a result, now that they are affecting the rich countries of the North, there is more funding for research into these diseases. We know them better and better, and the authorities are also reacting. These diseases are subject to mandatory reporting even if, for the moment, no deaths directly linked to these infections have been documented in mainland France.
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