X marks the spot: How to get mosquitoes to breed themselves to death

X marks the spot: How to get mosquitoes to breed themselves to death

Jun 14th 2014 | From the print edition

KILL the mosquito and you kill the disease. That is the usual approach to controlling malaria. And if done properly, it works. The problem is that the insecticides employed to do the killing destroy lots of other things as well. An old dream of those who seek to eliminate malaria is thus a way of selectively killing only what transmits the parasite: mosquitoes of the genus Anopheles, most notably Anopheles gambiae. And that, more or less, is what is proposed by Nikolai Windbichler and Andrea Crisanti of Imperial College, London, in a paper in Nature Communications. They think they have worked out how to stop A. gambiae females being created in the first place. That would break the chain of transmission in two ways: immediately, because it is only females that drink blood and so pass the parasite on; and in the longer term because without females a population cannot reproduce.

The researchers’ trick is to engineer into the mosquitoes a gene for a protein called a homing endonuclease. These genes are peculiar, and are probably a type of genetic parasite. They cut particular sequences of DNA in a way that damages the chromosome such DNA is found in. In extreme cases, that destroys the chromosome. (In less extreme cases, the process of repair often copies the endonuclease gene into the repair site; hence the name “homing”, and also the suspicion of parasitism). Dr Windbichler and Dr Crisanti have found a homing endonuclease in a species of slime mould that, by a strange coincidence, cuts a sequence of DNA found repeatedly in the X chromosome of Anopheles gambiae, destroying the chromosome completely.

Like humans, mosquitoes with two X chromosomes are female and those with an X and a Y are males. An unfertilised egg can therefore have only an X chromosome, but a sperm cell can have either. It is thus the sperm that determines an offspring’s sex. By transplanting the endonuclease gene into the genomes of male mosquitoes, and arranging for it to be active only during the process of spermatogenesis (so that other bodily functions are unaffected), the researchers create males which produce predominantly “male” sperm cells—about 95% of them carry Y chromosomes. Many of these will also carry the endonuclease, so the same thing will happen in the next generation. The upshot is that a population into which the modified males are introduced should get more and more male-dominated, and smaller and smaller.

That was certainly the case in caged populations the researchers experimented on. Whether it will happen in the wild will depend on whether female mosquitoes can tell the difference between normal and modified males. If they cannot, then releasing a bunch of modified males into an area might, at least temporarily, break the chain of transmission.

Eventually natural selection will find a way around the endonuclease, and the number of mosquitoes will return to normal. But if the parasite has gone, and is not reintroduced from elsewhere (as sometimes happened in places made malaria-free using insecticides), then a malaria-free zone will have been created without much disruption to the local ecology.



About bambooinnovator
KB Kee is the Managing Editor of the Moat Report Asia (, a research service focused exclusively on highlighting undervalued wide-moat businesses in Asia; subscribers from North America, Europe, the Oceania and Asia include professional value investors with over $20 billion in asset under management in equities, some of the world’s biggest secretive global hedge fund giants, and savvy private individual investors who are lifelong learners in the art of value investing. KB has been rooted in the principles of value investing for over a decade as an analyst in Asian capital markets. He was head of research and fund manager at a Singapore-based value investment firm. As a member of the investment committee, he helped the firm’s Asia-focused equity funds significantly outperform the benchmark index. He was previously the portfolio manager for Asia-Pacific equities at Korea’s largest mutual fund company. KB has trained CEOs, entrepreneurs, CFOs, management executives in business strategy, value investing, macroeconomic and industry trends, and detecting accounting frauds in Singapore, HK and China. KB was a faculty (accounting) at SMU teaching accounting courses. KB is currently the Chief Investment Officer at an ASX-listed investment holdings company since September 2015, helping to manage the listed Asian equities investments in the Hidden Champions Fund. Disclaimer: This article is for discussion purposes only and does not constitute an offer, recommendation or solicitation to buy or sell any investments, securities, futures or options. All articles in the website reflect the personal opinions of the writer.

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