Scientists have modified a fungus to contain a gene derived from the venom of a spider to kill malaria-carrying mosquitoes in West Africa. The genetic duplicity worked, with most of the mosquitoes dead within two generations.

Billions of people live in regions where mosquito-borne diseases are a real and present danger. The heaviest burden is in sub-Saharan Africa, where more than 200 million cases of malaria are reported each year, according to the World Health Organization. While other genetic modification experiments are in the pipeline, none are quite like this one, said lead author Brian Lovett.

“No transgenic malaria control has come this far down the road toward actual field testing. This paper marks a big step and sets a precedent for this and other transgenic methods to move forward,” said Lovett, from the University of Maryland (UMD), in a statement.

The field test was conducted in a 6,550-square-foot structure with walls of mosquito netting rather than glass. The laboratory, called MosquitoSphere, was located in Burkina Faso, West Africa, where over 7.9 million cases of malaria were reported in 2017, and is one of the 10 "high-burden countries" unable to meet their WHO Global Technical Strategy targets.

The team used a fungus strain specific to mosquitoes and modified it to produce a toxin derived from the blue mountains funnel-web spider. This toxin is an EPA-approved insecticide called Hybrid already used on crops to control pests. 

"You can think of the fungus as a hypodermic needle we use to deliver a potent insect-specific toxin into the mosquito," said Raymond St. Leger, a professor of Entomology at UMD and co-author of the study published in the journal Science.

"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," added Lovett. "And it is as effective at killing insecticide-resistant mosquitoes as non-resistant ones.”

The next question is what happens to local insects exposed to the fungus? Preliminary testing suggests it’s not harmful to other insects such as honeybees, a much-needed species. The selective carnage is due to the fungus’ toxin remaining inactive until reaching the mosquitoes’ bloodstream.

"These fungi are very selective," said 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.”

In one experiment, the team applied sesame oil containing the fungus to black cotton sheets inside the sphere. They then released more than 1,000 Anopheles coluzzii mosquitoes that had fed from the blood of a calf. They compared the results of this population to a control population that had no fungi or fungi without toxin modification. Within two generations, their population levels crashed to just 13 adults. In another experiment, Hybrid-infected females laid just 26 eggs, compared to 139 eggs in the control group.

The results are promising but not yet ready for open field tests. Some researchers are concerned that genetic engineering of the fungus could result in a trickle down effect on the ecosystem. There are also regulatory hurdles to meet before the method can be used in regions like Burkina Faso.