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2 Billion Genetically Modified Mosquitoes Cleared for Release in California and Florida

The EPA has approved Oxitec's modified skeeters for release into the wild, as part of a strategy to reduce mosquito-borne diseases.

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A plastic container containing Aedes aegypti mosquitoes
A plastic container containing Aedes aegypti mosquitoes
Photo: Allison Shelley/For The Washington Post (Getty Images)

British biotech firm Oxitec announced this week that it has received approval from the U.S. Environmental Protection Agency for its genetically modified mosquitoes to be released in parts of Florida and in California, following the completion of a pilot program last year. The modified male insects are designed to produce infertile offspring, ideally reducing local populations and rates of mosquito-borne illness.

The male mosquitoes developed by Oxitec—codenamed species OX5034—are derived from Aedes aegypti, a notorious carrier of many diseases, including Zika, dengue, and yellow fever. When these mosquitoes mate with the native females in an area, they’re said to produce female larvae that simply die off before reaching adulthood, thus dooming the population as a whole. And because only female mosquitoes bite and suck blood from humans, the modified insects are thought to pose no danger to people.


Last year, following approval from the EPA and local authorities, Oxitec launched a pilot program to release millions of these mosquitoes in select areas of Florida, in collaboration with the Florida Keys Mosquito Control District. On Wednesday, Oxitec said that the EPA had issued an approval for the Florida program to continue, as well as approval for a new program in California. The EPA’s decision allows for more than 2 billion mosquitoes to be released across the two states.

“Our team is immensely proud to have received yet another milestone approval from the EPA. This expansion of our U.S. efforts reflects the strong partnerships we’ve developed with a large and diverse range of stakeholders at the local, state and national levels,” said Grey Frandsen, CEO of Oxitec, in a statement from the company.


Oxitec’s method is the latest example of what’s known as the sterile insect technique, which has previously been used to eradicate or reduce populations of other harmful pests, such as screw flies. But the program hasn’t come without controversy. Some residents in Florida have long protested the release of the mosquitoes, while some groups have maintained that they could pose unknown environmental or health risks. Others have argued that the EPA and local agencies haven’t done enough to ensure the complete transparency of the project.

A paper in September 2019 drew lots of attention for claiming to show that a small percentage of the offspring produced by Oxitec’s mosquitoes in Brazil had indeed survived and were spreading their genes to the rest of the population. But the paper was soon criticized by other scientists for a lack of compelling evidence supporting these claims, and an expression of concern from the journal’s editors, laying out many of these alleged flaws, was attached to the paper by March 2020.

Meanwhile, Oxitec’s released data has shown that its programs do significantly reduce the local mosquito population, and Brazil formally approved the use of these mosquitoes in 2020. The EPA, for its part, continues to state that the release of modified mosquitoes into communities is thought to pose no risk to people, animals, or the environment. Unrelated sterile mosquito programs elsewhere—using bacteria, not genes, to render male mosquitoes less fertile—have similarly shown success in reducing mosquito populations and rates of diseases like dengue.

While the EPA has signed off on Oxitec’s programs moving forward, the company will need additional permission from relevant local regulators, which isn’t necessarily a given. Despite having received the EPA’s go-ahead for a program in Texas to start in 2021, for instance, it ultimately didn’t happen.