Biology

Why millions of genetically engineered mosquitoes will be released in the US

Anthony James, who researches disease-spreading insects, never encountered the aggressive mosquito species, Aedes aegyptiwhen he grew up in Southern California decades ago.

“Now, they’re here,” James, a molecular biologist at the University of California, Irvine, told Mashable.

Aedes aegypti almost certainly traveled to California in cargo, like many invasive species do. The species, which flourishes in warmer climes, has colonized places like Los Angeles County, and is expected to multiply and spread in these temperate regions as the climate continuously warms. The invasive species has already thrived in the Gulf states for centuries. Crucially, Aedes aegypti aren’t simply an itchy annoyance (the females voraciously bite for blood meals): The mosquitoes spread viral diseases like dengue fever, yellow fever, Zika, among others.

Future outbreaks in new and old parts of the US have a realistic, unsettling potential. To prepare, the US Environmental Protection Agency recently allowed for the carefully regulated, experimental release of over 2.4 million genetically-modified mosquitoes in California and Florida over the next couple of years. It’s a pilot project intended to prove that Aedes aegypti populations can be repressed by genetically-altered mosquitoes. The modified mosquitoes are non-biting males carrying a manipulated gene that, after mating, kills the insects’ offspring. The biotechnology company Oxitec devised this mosquito-control strategy, and will run the tests.

With the Aedes aegypti encroachment a reality, biologists say it’s wise to prepare to control their unwelcome, and potentially harmful, spread. Importantly, they emphasize this novel mosquito control — a form of “biological control” because another critter is used to significantly curb the target population — comes with many advantages, but little risk.

“Now, they’re here.”

“We’ve already seen this invasive species invading the US and other regions,” Carrie Manore, an expert in mathematical epidemiology who researches diseases and ecological systems at Los Alamos National Laboratory,” told Mashable. Manore, along with James, has no involvement with the Oxitec project.

“It’s good that we’re thinking about ways to control and mitigate mosquito-borne diseases,” Manore added.

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The CDC’s best estimate of the range of the Aedes aegypti mosquito in the US
Credit: CDC

The benefits of using genetically-modified mosquitoes

The EPA cleared Oxitec to release their modified, male Aedes aegypti mosquitoes in two areas: In the city of Visalia, located in California’s Tulare County, and in parts of the Florida keys. The two pilot projects now just need state permission to start the biological control tests. (Florida already permitted an earlier Oxitec Aedes aegypti test in 2021.)

“Biological control is a great way to go,” emphasized James. Here are the merits of this biological control strategy:

1. Avoids spraying pesticides: When pest control agencies spray pesticides, they’re inevitably killing unintended species. “All these pesticides we’re spraying have serious collateral damage,” Sharon Bewick, an assistant professor of biological sciences at Clemson University, who also has no involvement with Oxitec, told Mashable. She noted, for example, that spraying insecticide to control for disease-carrying mosquitoes in South Carolina killed millions of bees. Globally, many insect species, the foundation of our food web, have declined due to a quadruple-whammy of habitat loss, agricultural pollutants, insecticides, and climate change. More pesticides won’t help. “Every time you take an imperiled population and hit it with a pesticide, a pesticide is not a good plan,” Bewick emphasized.

What’s more, mosquitoes like Aedes aegypti evolve over time and have built up genetic resistance to different insecticides, making the chemical sprays a weaker pest-control strategy. “You have to spray all the time, and then you’re stuck dealing with resistance,” noted James.

“All these pesticides we’re spraying have serious collateral damage.”

2. Not harming native species: The Oxitec mosquitoes aim to only kill the invasive species Aedes aegypti. It’s true that native mosquitoes, while annoying pests to us, play a vital role in the natural food web. Birds, for example, devour mosquitoes. But Aedes aegypti aren’t a native species nor a critical player in the natural North American ecosystem. “They’re not part of any keystone species in some tightly-tuned ecological system,” said James. “They’re invasive.” Overall, the modified Aedes aegypti strategy has a quick, targeted, limited effect. The greater environment isn’t involved. “They mate, the babies die,” said Bewick.

3. They’re non-biting males: Only female mosquitoes bite. The modified mosquitoes are males, meaning the trials aren’t releasing more biting insects into places where people live.

The risks are low

Everything carries a certain level of risk. But the biologists Mashable spoke with found little to negligible risk associated with the modified Oxitec mosquitoes — provided the forthcoming trials work as planned.

“It’s fairly low risk,” said Los Alamos’ Manore.

Biologists have repeatedly heard concern over a potential, though perhaps misunderstood risk: When the engineered mosquitoes mate with females, perhaps not all the resulting offspring will always die. This means that some altered genes may get out into the wild mosquito world. But what does that really mean? It means some altered genes might be passed among Aedes aegyptibut at most it’s likely to have a harmful effect on these mosquitoes’ ability to reproduce.

These altered genes, which are specifically targeted to make mosquito eggs into duds, won’t somehow get passed to humans. “These genes are not passed onto people,” said James. “The biology doesn’t allow that at all.”

A potent tool in a heating climate

If the Oxitec trials prove effective, vector control agencies will have the choice to employ these modified mosquitoes to suppress Aedes aegypti — and the diseases they spread.

“There are lots of mosquito-borne pathogens out there,” said Manore. And while the burden of mosquito-borne diseases is higher in countries with developing economies, we definitely still have them in the US, she emphasized. West Nile Virus is the most common mosquito-borne illness in the Lower 48 states, with hundreds of reported cases annually.

And as the climate continues to warm, we should expect to see Aedes aegypti colonize more areas, particularly places where water is available for the mosquitoes to lay eggs. “Vector-borne pathogens are expected to emerge or reemerge due to the interactions of climate factors with many other drivers, such as changing land-use patterns,” the US Global Change Research Program concluded in a 2016 scientific assessment. Aedes aegypti just need a bottle cap’s worth of water to successfully lay eggs.

But we aren’t nearly helpless. “The impacts to human disease, however, will be limited by the adaptive capacity of human populations, such as vector control practices or personal protective measures,” the report said.

an Aedes aegypti biting a hand

An Aedes aegypti mosquito biting someone’s hand.
Credit: Joao Paulo Burini / Getty Images

In places like California, where the worries of Dengue fever are far-off, all that’s needed is someone to get off a plane and bring in the disease. Then, Aedes aegypti can spread it. “You could potentially have an outbreak,” James said. “Just saying we don’t have it here is not a defense.”

Already, Aedes aegypti are biting more people in Los Angeles, a city once free of the aggressive species. Other Southern California areas are now warning residents to watch for these voracious biters.

They like the warmth here. And we give them plenty of water to thrive in our gardens, sewers, and agricultural areas. It’s an Aedes aegypti dream.

“It’s like they’ve gone to heaven,” said James.

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