A genetically modified fungus designed to safely reduce malaria-spreading mosquito populations has, for the first time, been successfully tested outside of laboratory conditions in a simulated village environment in Burkina Faso, West Africa. The trial decimated the target mosquito population in only 45 days, paving the way for more trials in open environments.

The project was inspired by the observation that fungus spores can land on the surface of an insect and ultimately infect, or kill, its host. In terms of efficiency fungus spores are not the best way to kill mosquitos though. In real world scenarios it generally takes quite a few spores to finally take down a mosquito.

So the researchers worked to supercharge the toxicity of a type of fungus called Metarhizium pingshaensei, a natural killer of disease-carrying mosquitoes including Anopheles gambiae and Aedes aegypti. The fungus was genetically engineered to express toxins from the North African desert scorpion and from the Australian Blue Mountains funnel-web spider.

Prior testing showed the fungus to be effective in killing the targeted mosquitos, but most importantly, the fungus was not harmful to other species such as honeybees. The fungus cleverly knows to only specifically penetrate mosquitos and ignore other species.

"These fungi are very selective," says co-author on the new research, Raymond St. Leger. "They know where they are from chemical signals and the shapes of features on an insect's body. The strain we are working with likes mosquitoes. When this fungus detects that it is on a mosquito, it penetrates the mosquito's cuticle and enters the insect. It won't go to that trouble for other insects, so it's quite safe for beneficial species such as honeybees."

This new trial tested the fungi in a controlled outdoor environment in a rural, malaria-endemic area of Burkina Faso. A large screened-in structure was constructed, called the MosquitoSphere. Inside the structure were three huts, with three different simulated scenarios. One hut contained no fungi, another held non-engineered fungi, and the final hut contained the genetically engineered fungi.

Inside each hut 1,000 adult male and 500 adult female mosquitoes were released, and for the next 45 days the researchers counted the number of insects each day. After 45 days there were just 13 adult mosquitos alive in the hut with the transgenic fungus, which is an insufficient number for a swarm necessary for breeding to be created. In comparison, there were 455 mosquitoes in the hut with the non-engineered fungi, and 1,396 mosquitoes in the hut with no fungus at all.

"Simply applying the transgenic fungus to a sheet that we hung on a wall in our study area caused the mosquito populations to crash within 45 days," explains Brain Lovett, lead author on the new study. "And it is as effective at killing insecticide-resistant mosquitoes as non-resistant ones."

Unlike other more aggressive methods such as gene drives, which infect mosquitos with engineered sterility genes to literally drive a local population into extinction, this technology is designed to temporarily reduce specific populations and stop broader malarial outbreaks. The researchers suggest caution moving forward of course, and regulatory benchmarks will have to be met before the fungus is tested in open environments.

The new research was published in the journal Science.

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