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
Kee Koon Boon (“KB”) is the co-founder and director of HERO Investment Management which provides specialized fund management and investment advisory services to the ARCHEA Asia HERO Innovators Fund (, the only Asian SMID-cap tech-focused fund in the industry. KB is an internationally featured investor rooted in the principles of value investing for over a decade as a fund manager and analyst in the Asian capital markets who started his career at a boutique hedge fund in Singapore where he was with the firm since 2002 and was also part of the core investment committee in significantly outperforming the index in the 10-year-plus-old flagship Asian fund. He was also the portfolio manager for Asia-Pacific equities at Korea’s largest mutual fund company. Prior to setting up the H.E.R.O. Innovators Fund, KB was the Chief Investment Officer & CEO of a Singapore Registered Fund Management Company (RFMC) where he is responsible for listed Asian equity investments. KB had taught accounting at the Singapore Management University (SMU) as a faculty member and also pioneered the 15-week course on Accounting Fraud in Asia as an official module at SMU. KB remains grateful and honored to be invited by Singapore’s financial regulator Monetary Authority of Singapore (MAS) to present to their top management team about implementing a world’s first fact-based forward-looking fraud detection framework to bring about benefits for the capital markets in Singapore and for the public and investment community. KB also served the community in sharing his insights in writing articles about value investing and corporate governance in the media that include Business Times, Straits Times, Jakarta Post, Manual of Ideas, Investopedia, TedXWallStreet. He had also presented in top investment, banking and finance conferences in America, Italy, Sydney, Cape Town, HK, China. He has trained CEOs, entrepreneurs, CFOs, management executives in business strategy & business model innovation in Singapore, HK and China.

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