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Aedes aegypti mosquito feeding on a human. (Image: The Centers for Disease Control and Prevention)

Aedes aegypti mosquito feeding on a human. (Image: The Centers for Disease Control and Prevention)

I remember first learning about Oxitec’s genetically modified (GM) mosquitoes several years ago. I was an entomology undergraduate sitting in my Insect Physiology seminar and, to be perfectly honest, the whole concept was a little over my head at the time. I was trying to wrap my brain around how genetic modification worked and what all of this would mean for the future as we entered this new age of molecular biology applications.

Since then, I’ve stayed up to date with Oxitec and this novel mosquito control project which utilizes genetically modified mosquitoes. Every now and then I’d see this story pop up in the media, but this time it seems to have gotten out of hand with news outlets, especially now that Oxitec is attempting to get FDA permission to release their GM mosquitoes in the Florida Keys.

Over the past week or so, I’ve seen a lot of misinformation and vitriol about this matter online. There are now several write-ups on GM mosquitoes (see a couple of good ones by Entomology Today and Christie Wilcox), so what I hope to do is sum up the key points and address some of the concerns that I see repeatedly pop up in the comment threads.

TL;DR: This GM mosquito program works at reducing wild Ae. aegypti mosquito populations and it is safe to animals, humans, and the environment. However, it probably won’t be an end-all solution to stop diseases vectored by mosquitoes.

So here we go, some key points and concerns that keep popping up:

#1: If genetically modified mosquitoes crash the population, what will the impacts be on the ecosystem? What about animals higher in the food chain like bats and birds that eat mosquitoes?

I’m happy that this is one of the first concerns that I see pop up near the top of online threads; it shows that the public is thinking about the big picture when removing an organism from a habitat. Mosquitoes can indeed be important pollinators and a food source for insectivores. But in the case of Oxitec’s GM mosquitoes, there would be no impact on other plants or animals in the Florida Keys.

It’s important to note that there are over 3,000 species of mosquitoes in the world, and Oxitec’s program seeks to reduce the population of just one species: Aedes aegypti. This mosquito is invasive to the Americas and no native predator’s diet consists primarily of Ae. aegypti.

Bats are often brought up on this issue because in temperate areas these animals are almost exclusively insectivorous. But the food items identified in their diet are primarily beetles, wasps, and moths; mosquitoes have comprised less than 1% of gut contents of wild caught bats in all studies to date. The same likely goes for native birds, fish, and frogs: Ae. aegypti does not make up the majority of their diets, which makes sense as this mosquito is just one invasive species and many of the insectivorous animals mentioned are generalists. As such, this invasive mosquito is not likely to be a significant pollinator in Florida.

Reducing or eliminating invasive Ae. aegypti populations in a location like the Keys will not impact the native insectivores. Pesticides, on the other hand, do cause off-target impacts to the ecosystem and native animals. Current control methods still involve pesticides to keep mosquito populations down, so GM mosquito releases in this case have the potential to reduce the need for broad pesticide applications, and thus reduce negative environmental impacts. So what would happen if a mosquito like Ae. aegypti were to be eliminated from the Keys? Life would go on.

#2: This genetic engineering technology is in its infancy and we don’t know all the potential outcomes or long-term effects.

Genetic engineering is a relatively new technology, but directed manipulation of DNA by humans outside of conventional breeding or mutations has existed since the 1970s. In that time, we’ve learned a lot about genetics and molecular biology applications to solve problems. For instance, human insulin for diabetic medication is produced by genetically-engineered microbes.

As Entomology Today points out, this GM mosquito control concept is not too different from the Sterile Insect Technique in which male insects are mass reared and sterilized through radiation. Thus when the males are released and mate with wild females, no progeny are produced and the population declines. This method of pest control is really ingenious: it is species-specific, it causes no adverse effects to the environment, and it works. It did an incredible job of eradicating the screwworm from the United States. Never heard of the screwworm? Exactly. If you Google search it, you’ll be glad it’s gone.

Instead of blasting bugs with radiation to sterilize them, we now have the technology to insert genes in the male insects that keep them physically fit but make their offspring die, leaving the same effective result of reducing the pest population. So what are the potential outcomes of this GM mosquito program? These are the only two legitimate scenarios that I can think of:

1) Male Ae. aegypti mosquito gets released. He gets eaten, squished, or dies of natural causes. Environment is the same.

2) Male Ae. aegypti mosquito gets released. He mates with a wild female Ae. aegypti mosquito. Her progeny die because of the autocidal gene from the GM male. Mosquito population is reduced.

#3: Why would we need GM mosquitoes produced by a private company? We already have mosquito control programs that work.

Many places in the U.S. have perfect conditions for some diseases like dengue to come roaring back. In South Florida, cases of dengue are already popping up. The Ae. aegypti mosquito is already there, and classic control methods cannot entirely abolish this urban-associated pest. Even with the best care, pesticide applications inevitably have some off-target effects. The most clever aspect of this GM mosquito control program is this:

There is nothing better at finding a female mosquito than a male mosquito

This is really why this concept works so well. The male mosquito doesn’t take blood meals. He doesn’t do much besides search for and find a female mosquito to mate with. Inserting a lethal gene into this pest species is essentially like making tiny mosquito-seeking missiles. It’s pretty clever and again, similar in concept to the sterile insect technique. There is really no way that we can eliminate all the mosquito breeding sites or eradicate mosquitoes with pesticides that don’t harm other living things. But in conjunction with current mosquito control methods, this could help to specifically target Ae. aegypti populations and reduce some of the need for pesticide applications.

Conclusion

So are Oxitec GM mosquitoes our complete saviors? Probably not. At the end of the day, for any pest management program, it is important to consider all options and alternatives. Potential techniques to reduce mosquitoes or mosquito-vectored diseases include:

  • vaccinations against mosquito-vectored diseases (if they exist and are available)
  • insecticide-treated bed nets
  • odor-baited insecticide traps
  • indoor spraying
  • pesticides applied to water where mosquitoes breed
  • infecting mosquitoes with bacteria (Wolbachia) that preclude the parasite transmission
  • more modern houses with solid roofs and screens
  • modification of the habitat so it is less suitable for mosquito production
  • genetically engineered (transgenic) mosquitoes

As with most complex issues that we face, reliance on a single tactic is unlikely to be sustainable in the long run. In the case of mosquito control, multiple tools will be needed to manage these insects and the diseases they vector. This program put forward by Oxitec to use GM mosquitoes has been shown to be effective in previous trials and from what I can tell there are no apocalyptic-scenario drawbacks like some media outlets would have you believe. Blind acceptance of this program is not the answer, but neither is unadulterated fear. Be critical, skeptical, AND open-minded, but think for yourself.

Below you’ll find some peer reviewed papers and other resources.

(This post originally appeared on The Next Gen Scientist. It has been reprinted with permission.)

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