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One study suggests that a fungus – genetically enhanced to produce spider toxin – can quickly kill a large number of mosquitoes that spread malaria.
The trials, which took place in Burkina Faso, showed that mosquito populations collapsed by 99% within 45 days.
The researchers said their goal was not to make the insects disappear, but to help stop the spread of malaria.
The disease, which spreads when female mosquitoes drink blood, kills more than 400,000 people a year.
Around the world, there are about 219 million cases of malaria each year.
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Researchers at the University of Maryland in the United States and at the IRSS research institute in Burkina Faso first identified a fungus called Metarhizium pingshaense, which naturally infects Anopheles mosquitoes that spread the malaria.
The next step was to improve the mushroom. "They are very malleable, you can manipulate them genetically very easily," Professor Raymond St Leger of the University of Maryland told BBC News.
They turned to a toxin found in the venom of a species of funnel spider in Australia.
Genetic instructions for making the toxin have been added to the genetic code of the fungus so that the fungus starts making the toxin once inside a mosquito.
"A spider uses its fangs to pierce the skin of insects and inject toxins.We have replaced the fangs of the spider with Metarhizium," says Professor St Leger.
Laboratory tests showed that the genetically modified fungus could kill faster and that fewer fungal spores were needed to get the job done. The next step was to test the fungus in conditions as close as possible to reality.
A fake village of 6,500 square feet – including plants, huts, water sources and food for mosquitoes – was established in Burkina Faso. He was surrounded by a double layer of mosquito net to prevent any flow.
The fungal spores were mixed with sesame oil and wiped on black cotton sheets. The mosquitoes had to land on the sheets to be exposed to the deadly fungus. The researchers started the experiments with 1,500 mosquitoes.
The results, published in the journal Science, showed that numbers skyrocketed when insects were left to fend for themselves. But when the spider-toxin fungus was used, there were only 13 mosquitoes left after 45 days.
"The transgenic fungus has quickly destroyed the mosquito population in just two generations," said Dr. Brain Lovett, of the University of Maryland.
The tests also showed that the fungus was specific to these mosquitoes and did not affect other insects such as bees.
He added: "Our technology is not intended to cause the extinction of mosquitoes, but our goal is to stop the transmission of malaria in a region."
New tools are needed to fight malaria because mosquitoes are becoming more resistant to insecticides. The World Health Organization warned that cases are increasing in the 10 most affected countries in Africa.
Professor Michael Bonsall of Oxford University commented on the results: "Well cared for – this is an extremely stimulating study.
"The chances of controlling mosquitoes with the help of this modified fungus are high.
"Proportionate biosafety regulations are needed to ensure the sustainability of this approach and other approaches to vector control. [mosquito] control using genetic methods are not lost by overzealous restrictions. "
Dr. Tony Nolan from the School of Tropical Medicine, Liverpool, added, "These results are encouraging.
"We need new and complementary tools to improve existing control methods, which are affected by the development of insecticide resistance."
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