Do GMO mosquitoes designed to eradicate Zika pose unique environmental risks?

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The Zika virus, parasites that cause malaria, and yellow fever, and a host of other diseases are all spread among humans by mosquitoes. So, couldn’t we just eradicate the mosquito?

Mathematically, it might be possible. Of the 3,500 species of mosquitoes that exist on the planet, only a hundred or so bite humans. Even fewer of those spread disease. Maybe we could just focus on eradicating this smaller subset.

While scientists usually don’t advocate for eradicating an entire species, in this case, some are saying we could make an exception. Biologist Olivia Judson has long supported the idea that, “we should consider the ultimate swatting.” And on local levels, this has already happened. The yellow fever mosquito Aedes aegypti was wiped out in the Panama Canal area by the early 1900’s, and a larvicide eliminated the presence of the malaria-parasite vector, Anopheles gambiae, in Brazil in the 1940’s.

These efforts required a huge amount of labor, the application of significant chemicals (including the now-banned DDT), and arguably resulted in significant environmental damage. Today, researchers are looking at genetic and physiological means to control and/or eliminate disease-carrying mosquitoes. For example, the company Oxitec has developed a method using a genetically modified sterile male to reduce mosquito populations. Other control methods include using CRISPR-Cas9 gene editing to precisely insert a gene that resists the Plasmodium parasite that causes malaria.

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An ecologically important buzz

But mosquitoes play an important ecological role: They provide food for migratory birds and the bug’s aquatic larvae make for an easy meal for fish and other predators.

In the Arctic, some ecologists have seen a kind of “butterfly effect,” in which swarms of summer mosquitoes can direct the paths taken by caribou herds, who create new trails to avoid the swarms, eating lichen, feeding wolves and thus altering the landscape of Arctic valleys.

Other scientists don’t see such a huge role for mosquitoes and some believe that other insects can fill the roles currently occupied by mosquitoes. Wildlife biologists have noticed that mosquitoes do not make up a significant part of bird diets in the arctic. And in other areas, when faced with a choice between a mosquito and a protein-rich moth, a bird will go for the moth.

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And then there are scientists who think that eliminating the mosquito might be the right bark but up the wrong tree. Grayson Brown, director of the University of Kentucky’s Public Health Entomology Lab, said recently that:

Malaria was a serious problem in North America until it was eradicated in the early 1950’s. The mosquito that vectored malaria in the US is the common malaria mosquito, Anopheles quadrimaculatus, and it is still a very common mosquito here. However, the specific strain of malaria that was well adapted to transmission by that mosquito is now gone. Malaria will only return to the US if another malaria strain arises that is adapted to one of our mosquitoes or if a malaria-transmitting mosquito invades the US.

Pathogen-carrying mosquitoes are all our fault

Related article:  Viewpoint: CRISPR crops have a chance to avoid the trust issues that plague GMOs

So, where did the pathogen-carrying mosquito come from? It turns out, it adapted to us, and the parasite it carried also promoted genetic adaptations that opened the door to a whole new feeding reservoir: humans.

The tropical mosquito, Anopheles gambiae, went through a rapid series of adaptions in response to environmental changes, most of which were created by humans. As we started to develop complex societies based on villages, towns, and farming, we created reservoirs (wet ones, mostly) that turned out to be perfect breeding grounds for mosquitoes. At the same time, the Plasmodium parasite that causes malaria also triggered changes in the mosquito immune system, effectively creating the an ideal environment for its survival.

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And a few dozen species (there are 500 species of Anopheles) became the perfect vector. They preferred human blood (and all mosquitoes are exquisitely built for sucking it in), could tolerate a parasite infection, lived long enough to reproduce and spread the parasite, and bred like crazy. And then came humans. As a group of entomologists from University of California, Riverside and University of Notre Dame wrote,

A trigger for the repeated emergence of human malaria vectors in different anopheline lineages may have been the growth of Neolithic human populations following the development of agriculture.

In the U.S., we got rid of malaria by attacking the mosquito but it was the parasite that was eventually eliminated. Some scientists think that even if we could get rid of Aedes aegypti or similar species, other species might take over. Phil Lounibos, ecologist at the Florida Medical Entomology Laboratory, found that female yellow fever mosquitoes (A. aegypti) that were inseminated by Asian tiger mosquitoes (A. albopictus), sterilized the A. aegypti mosquitoes. Since the tiger mosquitoes carry several human diseases, this suggested that another pathogenic mosquito could take over even if A. aegypti were eliminated.

So, while we might be able to rid ourselves of the pathogen that causes disease, we and the mosquito might be stuck with each other.

Andrew Porterfield is a writer, editor and communications consultant for academic institutions, companies and non-profits in the life sciences. He is based in Camarillo, California. Follow @AMPorterfield on Twitter.

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