In late April, the biotechnology company Oxitec placed blue-and-white hexagonal boxes on the properties of six private volunteers around the Florida Keys. After pouring in water, the genetically modified mosquito eggs inside activated and hatched.
Now the first larvae have developed into full-grown male mosquitoes and taken flight, Susan Millis reports for Science News. About 12,000 of Oxitec’s male mosquitoes will fly out of the boxes each week for the next 12 weeks.
Over several mosquito generations, Oxitec’s genetically modified Aedes aegypti could reduce the population of female mosquitoes—which bite and spread disease—and then lower the entire population in the Florida Keys in turn. The current trial marks the first time that genetically modified mosquitoes have been released to fly freely in the United States.
It also comes just after the largest outbreak of dengue in the Florida Keys since 2010.
“Dengue was something we worried about in other areas,” says Andrea Leal, the Florida Keys Mosquito Control District’s executive director, to Gwen Filosa at the Miami Herald. “Once that came to our doorstep we’ve seen other diseases. Dengue for us last year and Zika in Miami-Dade. This is really why we’re looking at these new tools for mosquito control.”
Oxitec is only releasing male mosquitoes, which don’t bite. They sport extra-fluffy antennae to catch the attention of wild female mosquitoes of the same species. When a genetically modified male mates with a wild female, their offspring will inherit the male’s modified DNA. Female offspring will be doomed to die as larvae, and male offspring will be a mix of some that can have normal offspring, and some that can only have male offspring.
The female offspring of the genetically modified males become reliant on an antibiotic called tetracycline to live. Scientists at Oxitec can provide tetracycline in the lab in order to keep females alive and breed more of the modified mosquitoes. But the chemical is uncommon outside of labs, which is why the females die as larvae, before they join the human-biting adult female mosquito population.
And Ae. aegypti females bite a lot of people—about half of their diet is human blood, says University of Southern Mississippi aquatic ecologist Don Yee to Science News. In the tropics, they seek out human environments, he adds, “The adults are literally resting on the walls or the ceiling. They’re hanging around the bathroom.”
Ae. aegypti carry about three dozen diseases, including dengue, Zika, yellow fever and chikungunya. While some opponents of the experiment have raised concerns about the environmental impact of removing the species, there are thousands of mosquito species, and make up only about four percent of the mosquito population in the Florida Keys.
“Oxitec is not trying to eliminate all mosquitoes. [The company is] getting rid of one mosquito species from a localized population to stop it from transmitting pathogens to humans,” says University of California, San Diego molecular biologist Omar Akbari to Donavyn Coffey at Scientific American. “And this mosquito species—A. aegypti—is invasive and doesn’t have a purpose in this environment. So I don’t think there will be any negative environmental impact from removing the species from the environment.”
The Oxitec mosquito trial had been under consideration in the Florida Keys for about a decade before it was approved. The plan faced vocal opposition from those who considered the approval process unfair to local concerns, Taylor White reports for Undark. Critics also raised concerns about the company not releasing any data about a reduction in disease; Kevin Gorman, Oxitec’s chief development officer, tells Undark that the company is not required to report formal health impact studies.
Those who oppose the release of modified mosquitoes have even threatened to derail the experiment by spraying insecticide in the Oxitec boxes. But there was also enough support for the program that the company was “oversubscribed” with people offering to host the mosquito boxes on their property, Oxitec’s chief of regulatory affairs Nathan Rose tells Science News.
“As you can imagine, emotions run high, and there are people who feel really strongly either for or against it,” says molecular biologist Natalie Kofler, the founder of Editing Nature, an advocacy organization focused on oversight and responsible development of gene-editing technologies, to Emily Waltz at Nature News. “And I can see how, if you didn’t agree to this, it could be really concerning to have mosquitoes released in your neighborhood.”