Transgenic Metarhizium rapidly kills mosquitoes in a malaria-endemic region
Nebert, Daniel (nebertdw)
Thu 6/20, 2:07 PM
The topic of today’s GEITP article is using a genetically-modified organism (GMO) to control a pest; this is an interesting “gene-environment interactions” type of story. Burkina Faso is a landlocked country in West Africa — surrounded by six countries that include Ivory Coast to the southwest. Mosquito-borne malaria is a serious health hazard there, and insecticide-treated bed nets had been working. However, as mosquitoes develop resistance to widely used insecticides, the nets have become less effective. Researchers have now chosen a new line of attack: testing a genetically modified fungus that kills malaria-carrying mosquitoes.
Authors [see attached article & editorial] built a 600-square-meter structure (called the MosquitoSphere), shaped like a greenhouse but with mosquito netting instead of glass. The sphere comprised six compartments — four of which contained WHO-experimental huts for West Africa sugar sources (plants) for adult mosquitoes, and breeding sites (plastic sheets buried in a layer of soil to allow water to be collected) — enclosed in a greenhouse frame with walls of mosquito netting to allow exposure to ambient climate conditions and simulate a natural mosquito habitat. Insecticide-resistant Anopheles coluzzii mosquitoes for these experiments were collected as larvae from local breeding sites and reared to adulthood in one compartment of the sphere. The sphere was purposely built to compare efficacy of Mp-Hybrid co-expressing green fluorescent protein (GFP) with that of Mp-RFP, a strain with wild-type virulence expressing red fluorescent protein (RFP), against A. coluzzii mosquitoes.
The fungus Metarhizium pingshaense provides an effective, mosquito-specific delivery system for potent insect-selective toxins. Based on previous studies, authors had found that suspending the Metarhizium in locally produced sesame oil, and spreading the suspension on black cotton sheets, achieves a long-term effect in the sphere; also, these sheets provide a resting area for mosquitoes that have taken blood meals from calves in the huts. In initial experiments, authors released 100 female insecticide-resistant A. coluzzii mosquitoes into each hut at dusk, allowed them to blood-feed from a calf, and then collected them the next morning to monitor fungal infections. In seven replicates — with cloths rotated between each compartment — authors individually collected a total of 2,402 mosquitoes and recorded their feeding status and location of capture. Of the mosquitoes recaptured the next morning, 93.2% were blood-fed. Throughout all the experiments, none of the mosquitoes that had been collected from the compartments containing control sheets were infected with fungus.
The GMO fungus eliminated 99% of the mosquitoes within a month. The fungus is a long way from real-world use: because it is genetically modified to make it more lethal, it could face steep regulatory obstacles. However, the fungus also has clear advantages because it spares insects other than mosquitoes, and because it doesn’t survive long in sunlight, it’s unlikely to spread outside the building interiors where it would be applied. Authors conclude that, because Hybrid-expressing M. pingshaense is effective at very low spore doses, its efficacy lasted longer than that of the unmodified Metarhizium. Deployment of transgenic Metarhizium against mosquitoes (subject to appropriate registration) could be rapid, with products that could synergistically integrate with existing chemical control strategies to avoid insecticide resistance. 😊
Science 31 May 2o19; 364: 894-897 & editorial (p. 817)