REPORTING. Malaria, dengue fever, chikungunya… Are bioinsecticides a solution to increasingly resistant mosquitoes?

In Cameroon, products based on combinations of plants are in the research phase. These nature-inspired insecticides could be used in France, where insect resistance to chemical repellents is also increasing.

For almost a month, Cameroon has been the first country in the world to vaccinate babies on a large scale against malaria, a disease transmitted by mosquitoes which will kill 600,000 people worldwide in 2023 in 250 million cases. Vaccines provide hope for the future but at the same time, the fight against mosquitoes remains a priority to combat the disease. The problem is that in Cameroon mosquitoes are increasingly resistant to insecticides.

Researchers are mobilizing to find alternatives, like Agnès Antoinette Ntoumba, who has been testing in her laboratory for five years combinations of plants individually already known to be effective against mosquito larvae: lemon, lime and orange tree, or even guava and leaves of moringa, a local plant. The idea is to create several recipes. “The objective is to be able to explore the flora of Cameroon because we have a very large flora and we hope that those who are in the west of the country do not need to come and look for plants that are in the south to be able to produce this bio-insecticide”, explain the teacher-researcher in parasitology and entomology.

“We are still carrying out several tests of different plants which could still be the subject of several associations.”

Agnès Antoinette Ntoumba, teacher-researcher in parasitology and entomology

at franceinfo

These insecticide recipes to spray on larval breeding sites must be inexpensive, available and accessible to all. “Even to you for example. I can show you how it is done and then make it for you to use tomorrow”, adds the entomologist. The originality of Agnès Antoinette Ntoumba’s research is to combine these combinations of plants with nanoparticles. These are small metal particles that will stimulate the effect of plants to kill mosquito larvae. “These are metal salts that we use for synthesis such as silver, zinc or gold salt because it kills all the larvae. There will then be a chemical reaction which is a reduction”. This reaction causes the metal to disappear. The insecticide then becomes organic.

Today, to equip her laboratory, Agnès Antoinette Ntoumba is chasing international funding grants. She could have gone to the United States, but prefers to stay in Cameroon. “This is where I’m needed, she answers. Because I would like to train students. And what I like is seeing young people who are mastering it.” The researcher’s next objective: to equip her laboratory in Douala with an insectary.

A growing question in France

On the French territory, if there is no presence of the malaria-carrying mosquito, there is now, almost throughout the territory, the tiger mosquito. This mosquito is a vector of other diseases which can also be fatal such as dengue, chikungunya and zika. Moreover, dozens of local cases occur every year, particularly concerning dengue fever.

The question of mosquito resistance to insecticides will also arise in France. This is confirmed by Grégory L’Ambert, entomologist at the Interdepartmental Agreement for Mosquito Control of the Mediterranean Coast. “Indeed, what I see is that all the products which will be used against adult mosquitoes today in France belong to the same family of insecticides, he explains. If we use these insecticides, not responsibly, inevitably, mosquitoes will end up being resistant to these products. This will pose a real problem since in the event of an epidemic we will no longer have effective tools to kill this adult mosquito and prevent the proliferation or spread of the disease.” The idea of ​​“homemade” insecticides like those being created in Cameroon is therefore promising.

“It’s indeed very interesting because insecticide products that are effective on mosquitoes often come from plants. The insecticide pharmacopoeia comes from plants. So it’s very interesting to have new possibilities.”

Grégory L’Ambert, entomologist at EID,

at franceinfo

Examples of naturally repellent plants exist in France. This is the case with pine needles. “They will acidify the water and can act as a natural insecticide, explains the entomologist. This is why we very very rarely find tiger mosquitoes under umbrella pines. It is therefore interesting to try to characterize these natural insecticides. he adds.

He also warns of the risks of seeing the proliferation of mosquitoes increase this year due to the mild winter temperatures. “What is certain is that for insect populations, cold winters are something that tends to limit the survival of the species and delay their development. So with the temperatures that the we have at the moment, this is not the case. Even if in July, we will perhaps not see the difference with a usual year, the risk is still to see the proliferation start a little more earlier than usual. The insect specialist recalls that mosquitoes are “a species which is capable of multiplying by 400 or 500 in a few weeks”. “So we prefer that she starts her activity as late as possible,” he adds.