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Here's Why Scientists Are Not Afraid of Genetically Modified Mosquitoes

In the first episode of our new series Scientificus, NBC News asks what's so scary about genetically engineered mosquitoes.

This is the first installment of a new series on called SCIENTIFICUS, where we'll lighten up the dark mysteries of science and medicine.

The Food and Drug Administration has said OK in principle to the release of genetically modified (GM) mosquitoes in Florida.

What could go wrong?

Aren’t GM mosquitoes a big suspect in all those birth defect cases in Brazil? A company called Oxitec released a bunch of those mosquitoes right before thousands of cases of a birth defect called microcephaly started showing up.

But the World Health Organization, Centers for Disease Control and Prevention and other experts are not worried about the little flies.

Related: What's Behind Those Bogus Zika Rumors?

They say the mosquitoes couldn’t possibly have caused birth defects. For one thing, the mosquitoes being genetically engineered by Oxitec are male. Male mosquitoes don’t bite. It’s the female mosquitoes that bite.

For another, the genetic changes are in the DNA of the mosquito — inside their sperm and eggs cells, not in their saliva.

Simple organisms such as bacteria can pass DNA back and forth directly. But it’s a lot harder for complex organisms to exchange DNA. That’s what sex is for. And scientists working to perfect gene therapy — a medical field aimed at correcting faulty DNA to cure disease — can attest to how difficult it is to get new DNA to take up residence in the human body.

The DNA change makes the mosquitoes die before they mature. So the GM male mosquitoes mate with females, which lay eggs that hatch, but the larvae die before they grow up.

The effect? A reduction of up to 90 percent in the local mosquito population.

Related: Natural Mosquito Repellents Don't Last

Another piece of evidence against the Zika rumors: The mosquitoes were released 600 miles from where the Zika outbreak started. Mosquitoes can only fly about 600 feet in their lifetimes.

Image: Genetically modified Aedes Aegypti mosquito pupae emerge
Genetically modified Aedes Aegypti mosquito pupae emerge, engineered by Oxitec. Oxitec

It’s the normal mosquitoes that are to blame for the horrendous birth defects. They’re the Aedes aegypti mosquitoes carrying Zika. Medical science has established how viruses like rubella cause birth defects and Zika is pretty clearly doing the same thing.

But what about the risk to the environment? Polls show that residents of the Florida Keys, where Oxitec wants to test its mosquitoes, worry that getting rid of mosquitoes will somehow damage the food chain.

Many experts argue that targeting only the harmful mosquitoes, the Aedes species that spread not only Zika but also the dengue and chikungunya viruses, is safer for the environment than overusing insecticides.And insecticides kill good insects, such as bees.

Plus mosquitoes can develop resistance to pesticides.

Related: CDC Watches Pregnant Women Infected With Zika

Not only that –there are 80 species of mosquitoes in Florida, so reducing populations of one of them isn’t going to starve any animals. In addition, Aedes mosquitoes are an invasive species, imported from Africa more than 100 years ago.

None of the experts believes GM mosquitoes are the only answer to controlling mosquitoes. But given the risks to human health – mosquito-borne illnesses kill 725,000 people every year – they argue it’s worth adding them to the arsenal.