Genetically Engineered Mosquitoes Won’t Conquer Malaria and Dengue—Yet

What's to come?
Nov. 14 2011 2:26 PM

GM Mosquitoes Bite

The critical problem with new experiments in using genetically engineered insects to fight malaria and dengue.

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The new generation of GM-mosquito researchers learned from the failed experiments of the ‘70s and ‘80s and is trying to assess the competitiveness of its modified insects in the wild. Alphey’s group found that the ones released in the Cayman Islands fathered about10 percent of the local eggs within a few weeks. They were about half as successful as wild mosquitoes, which sounds poor, but is actually better than a lot of other modified insects, including the successful sterile medflies. The team has suggested that it could compensate for the males’ shortcomings by simply releasing more of them.

Even if that works, it would still be better to make the GM mosquitoes as competitive as possible from the outset. The longer these programs run, the greater the odds that female mosquitoes will simply evolve to avoid the GM males. Again, there is historical precedent. In the 1970s, Japan tried to control the melon fly by releasing large numbers of sterile males. These efforts continued for many years before the females gained the ability to recognise and avoid the interlopers. The message is clear: We cannot afford a guerrilla war with disease-carrying insects. We need shock-and-awe tactics that have a big impact in a short period of time. And to achieve that, we need to plug the gap in our knowledge of mosquito ecology.

Unfortunately, Ferguson says, “A lot of the knowledge gaps that hindered previous attempts still remain.” In a recent review, she noted, “We have made substantially more headway in understanding the reproductive biology of species with no direct public health or economic importance, such as Drosophila, fur seals and blue tits, than we have done for this vector that kills millions.”

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This crucial ecological research on mosquitoes is trapped in a financial no-man’s land. Organizations that fund basic research into issues like how insects behave assume that biomedical agencies will foot the bill, while these agencies are more likely to prioritize research with more obvious and immediate clinical impact. But the necessary ecological studies would not be expensive. Ferguson estimates that it would take just $500,000 to fund 10 students in the field, an act that “could easily quadruple our knowledge of this area within a few years.”

For example, in 2008, her student Kija Mg’Habi worked in an isolated, malarious part of Tanzania and discovered that among Anopheles gambiae (a species that carries malaria), the medium-sized males get the most sex. You might expect the biggest males to outcompete their smaller rivals, but they were actually six times less successful. This is exactly the type of information you need if you want your modified mosquitoes to outcompete their natural brethren.

Now, several scientists are trying to learn more about mosquitoes by setting up “semi-field studies.” These large outdoor spaces, enclosed by nets, are like mosquito aviaries. They should allow scientists like Ferguson to study large numbers of mosquitoes, both normal and modified, under natural but controllable conditions. These studies will not only be useful as testing grounds for GM strains; they should also start to provide some long-missing information about our mosquito adversaries. It may not be as sexy as modifying genes, but ecology is tantamount to knowing your enemy, and that surely is a cornerstone of victory.

Ed Yong is a freelance science writer. He writes the Discover blog Not Exactly Rocket Science.

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