• An Improvised Genetic Death to Mosquitoes?

    Nature Biotechnology. September 24, 2018. doi:10.1038/nbt.4245

    In a history-making event, and a genetic first, researchers created a set of destructive genes that infiltrated small populations of mosquitoes and drove them to extinction. This death by deliberate manipulation of genes occurred in a lab in mosquito populations with less genetic diversity that an extinction scheme would face in the wild. Although a long way from real-world application, this represents a major step in wiping mosquitoes off the face of the Earth.

    Work done at Imperial College London focused on one of the main malaria-spreading mosquitoes, Anopheles gambiae, which is a mosquito that thrives and inflicts deadly consequences in much of sub-Saharan Africa. Here, an excess of 400,000 people a year die from malaria, representing 90% of the global total of malaria deaths!

    The researchers put together genes for a molecular copy-and-paste tool called a CRISPR/Cas9 gene drive. The gene drive, which in this case targeted a mosquito gene called double-sex, is a pushy cheat. It copies itself into any normal doublesex gene it encounters, so that all eggs and sperm will carry the gene drive into the next generations. Female offspring (the biters and disease inflicters) with two altered

    doublesex genes develop with male characteristics and are unable to bite and cannot reproduce.

    In the test, researchers set up two enclosures, each mixing 150 males carrying the saboteur genes into a group of 450 normal mosquitoes, males and females. Death to all, ie extinction, occurred in 8 generations in one of the enclosures and in 12 in the other.

    This is the first time that a gene drive has forced a mosquito population to breed itself down to zero, however the researchers caution that such extinctions will be much more difficult to achieve in the wild due to the genetic diversity and mutagenic activity that is seen that will likely result in genetic quirks that may counter such efforts.

    But what if a human-directed gene modification program could monkey-wrench a wild population, or maybe a whole species, all the way to extinction? Should people release such a thing?

    Estimating what difference it would make ecologically if a whole mosquito species disappeared has stirred up plenty of speculation but not many data. In framing a devil’s advocate role, the closest the researchers came to finding a predator that might depend heavily on this particular mosquito was the little East African jumping spider. It catches An. gambiae for about a third of its diet and likes the females fattened with a human blood meal.

    Some experts believe that saddling mosquitoes with gene drives to take down their own species is likely to have fewer ecological risks than broad-spectrum use of pesticides that also kill other species and beneficial insects. Stay tuned for future developments in the domain.

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