Mosquito-killing fungus enhanced with toxins

A new study suggests genetically modified fungus could help target mosquitoes and reduce incidences of malaria.

The fungus produces spider and scorpion toxins that act as a biological control mechanism for mosquitoes without affecting honey bees and other insects.

Brian Lovett, a graduate student from the University of Maryland and co-author of the study published in Scientific Reports, said: “Our most potent fungal strains, engineered to express multiple toxins, are able to kill mosquitoes with a single spore. We also report that our transgenic fungi stop mosquitoes from blood feeding. Together, this means that our fungal strains are capable of preventing transmission of disease by more than 90 percent of mosquitoes after just five days.”

Researchers used the fungus Metarhizium pingshaensei, which naturally kills mosquitoes. Previous research has shown that it is specific to disease-carrying mosquitoes, such as Anopheles gambiae and Aedes aegypti. Upon contact with a mosquito’s body, the spores germinate and penetrate the insect’s exoskeleton, eventually killing the insect host from the inside out.

Enhancing the fungus' potency

To improve the potency of the fungus, researchers engineered it with several genes that express neurotoxins from spider and scorpion venom. These toxins work by blocking calcium, potassium and sodium channels that allow nerve impulses to travel. The engineered strains were tested on wild-caught, insecticide-resistant mosquitoes in Burkina Faso and worked better than the unaltered fungus.

Professor Raymond St. Leger, from the University of Maryland and senior author, said: “The WHO has identified insecticide resistance as the major threat to effective mosquito control, which is relevant not only to malaria but to a number of mosquito-borne diseases such as dengue, yellow fever, viral encephalitis and filariasis. Unlike chemical insecticides that target only sodium channels, many spider and scorpion toxins hit the nervous system's calcium and potassium ion channels, so insects have no pre-existing resistance."

To ensure that the genes couldn’t be released in the environment or in other animals, a highly specific promoter sequence was inserted so the toxins would only be activated in insect blood. Tests were carried out on local bees by exposing them to the spores. After two weeks, no local bees died as a result of spore exposure. Lovett said: “This is our first in-depth study of the effects toxin-expressing fungi have on mosquitoes, beyond their ability to kill faster. This is also our broadest characterisation of our arsenal of insect-killing spider and scorpion toxins.”