Mosquitoes, hornets, stink bugs: life cycles change as France warms up

Invasive species are receiving a boost from climate change as they adapt their life cycles to the French seasons, research has found.

Tiger mosquitoes, asian hornets and stink bugs were not present in France fifty years ago. Today, however, all three species are present in vast numbers in most of the country.

Along with this plague of pests come new challenges and dangers:

• An association of beekeepers in Brittany recently warned about the dangers of asian hornets nesting in discreet holes in the ground.
• A case of dengue fever, which is spread by tiger mosquitos, was reported in Paris in October 2023
• Stink bugs, in addition invading homes with their foul smell, can cause allergic reactions.

For David Giron, director of the Institut de Recherche sur la Biologie de l'Insecte (IRBI), which studies insect biology, the spread of these pests is certainly related to climate change.

“It’s very clear that climate change has an impact on the persistence of their colonies,” he told Sud Ouest.

“Due to the warm autumn, asian hornets were reproducing as if it were summer. The result is more individuals and a greater population.”

Read more: Asian hornets are still prolific in France due to mild autumn

Tiger mosquitos, which typically begin to lay cold resistant eggs as the weather cools, can continue normal reproduction when the weather is fine.

“We now see an increasing number of generations per season, which is why the active population persists longer,” said Mr Giron.

Read more: Mosquitoes in France: A scientist's advice for keeping them away

Stink bugs are typically more noticeable as the weather begins to cool. However, it is during the summer that they reproduce, only seeking the shelter of people’s homes when they need to overwinter.

“It is likely that the weather conditions this summer helped that species too, which is why we are seeing so many of them this autumn.”

‘Some insects need cold weather’

While mosquitos can thrive all year round in warm conditions, others, such as butterflies require a hibernation phase.

“Such species require a diapause, and if the weather is not cold enough, then the species will not be in a position to create a new generation in spring, which would be catastrophic for them,” said Mr Giron.

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