Mosquitoes are responsible for transmitting some of the most notorious diseases that have ravaged and decimated human populations throughout the centuries, including malaria, zika, and yellow fever. Historically, these diseases were largely relegated to tropical and subtropical regions in Africa, Latin America, South Asia, and Oceania. However, climate change could allow mosquitoes populations to rapidly grow in cooler regions like Europe and Northern America, thereby enabling the spread of mosquito-transmitted diseases in these regions.

These diseases can have serious consequences on the people who contact them: Malaria and yellow fever can cause fever, headaches, nausea, vomiting, and (in the most severe cases) death—over 643,000 people were killed by malaria worldwide in 2019. Zika is known for causing pregnant women to give birth to children with microcephaly, a condition in which infants are born with underdeveloped heads and brain damage.

What are Genetically Engineered Mosquitoes?

Fortunately, one innovative solution has been proposed to reduce the mosquito population and prevent tropical diseases from spreading across the world: genetically engineered mosquitoes. Oxitec is a biotechnology company based in the United Kingdom that uses genetic engineering to counter the spread of mosquitoes with the goal of strengthening food security and protecting public health.

As part of a bold effort to control the mosquito population, Oxitec developed a genetically modified version of the yellow fever mosquito (Aedes aegypti), a species known to transmit a variety of mosquito-borne diseases, including yellow fever, Zika, West Nile virus, chikungunya, and dengue.

Male mosquitoes do not bite, which is why Oxitec uses them for its projects. Oxitec inserted a new gene into its bioengineered male Aedes aegypti mosquitoes. The gene passes on to the mosquitoes’ offspring and kills young female mosquitoes before they can complete their early larval stages. Oxitec hopes to release its genetically modified male mosquitoes into the wild where they can mate with female mosquitoes, which bite humans. These bioengineered insects have the potential to control mosquito populations and mosquito-borne diseases—all by producing a lost generation of female mosquitoes that never have the chance to reach sexual maturity.

Oxitec also modifies its mosquitoes’ genomes to make them glow when exposed to a certain color of light, which makes them easy to differentiate from wild mosquitoes whose genes have not been edited.

Genetically Engineered Mosquitoes in the Real World

Oxitec has tested out its genetically modified mosquitoes in warm tropical and subtropical regions of the world, with generally positive results.

In 2009 and 2010, Oxitec released its bioengineered Aedes aegypti mosquitoes onto the Cayman Islands, a British Overseas Territories consisting of islands in the Caribbean Sea. These tropical islands are prone to zika, chikungunya, and dengue, so to hinder the spread of these diseases on the islands, Oxitec released its genetically engineered male mosquitoes there. After Oxitec’s mosquitoes produced several generations of female mosquitoes that died before reaching sexual maturity, mosquito reproduction plummeted. As a result, the Aedes aegypti population fell by up to 90 percent in some parts of the islands.

In 2014, Oxitec sent its genetically modified mosquitoes to Panama, where the spread of dengue was a major concern at the time. Once again, the results were thrilling: Bioengineered males mated with wild females, the next generation of females failed to reach sexual maturity, and the mosquito population fell by 90 percent in some regions.

Oxitec began to release its mutant mosquitoes in Brazil in 2016 after 1.6 million cases of dengue ravaged the country in the previous year. The company began with the city of Piracicaba near São Paulo. After dispersing its genetically modified Aedes aegypti in other parts of Brazil over the next few years, Oxitec concluded that the mutant mosquitoes could reduce wild Aedes aegypti populations by up to 96 percent.

Obstacles That Lie Ahead

Despite the successes of Oxitec’s genetically engineered mosquitoes, there are still obstacles that may hamper their use in the future. For example, some scientists have been skeptical about Oxitec, claiming that its bioengineered mosquitoes could produce viable offspring with wild mosquito populations and alter the gene pool of those populations. A few researchers have voiced concerns that the mutant mosquitoes could accelerate the spread of tropical diseases like malaria. Oxitec has denounced these claims, noting that the data presented by those skeptical scientists shows no evidence that Oxitec’s genetically engineered mosquitoes have negatively impacted human populations.

In the United States, the Environmental Protection Agency (EPA) tightly regulates genetically modified organisms that are released into the wild. Due to burdensome regulatory hurdles, Oxitec had to fight for about a decade with the EPA before it could convince the agency to authorize the release of its mutant mosquitoes onto the Florida Keys in 2021.

Some local residents on the islands have strongly criticized the project for choosing their towns as test sites. A few people from the Florida Keys have threatened to spray insecticides on Oxitec’s bioengineered mosquitoes. Although regulators reauthorized Oxitec’s mutant mosquito project in the Keys about a year after it began, there has still been major pushback from locals who view the project as intrusive upon their hometowns.

Oxitec employees have tried to convince residents of the Keys that they should not worry since the mutant mosquitoes will produce female offspring that will always die before reaching sexual maturity. However, many locals remain skeptical about Oxitec’s claims and continue to worry about potentially negative consequences of the project.

Oxitec has also encountered regulatory barriers in California, where state legislators have urged regulatory authorities to prohibit the company from releasing its genetically engineered mosquitoes in the state. These legislators called for the release of the mutant mosquitoes in California to be delayed until tougher regulations are enacted, which they view as necessary to protect the safety of humans and the environment while ensuring that the project does not become impossible to manage.

Genetic engineering is a highly controversial technology, and it can provoke even more controversies if it is used to engineer entire ecosystems, like with Oxitec’s mutant mosquitoes. Supporters of Oxitec’s projects emphasize the scientific evidence that indicates that Oxitec’s bioengineered mosquitoes have made humans safer from tropical diseases by reducing Aedes aegypti populations. Opponents of these projects claim that the mutant mosquitoes may have unintended consequences on human and environmental health.

Ultimately, anyone can examine the evidence for themselves to determine whether genetically engineered mosquitoes are the right solution to dealing with mosquito-borne diseases. It is up to people like us to participate in these public policy debates, such as whether or not to allow companies like Oxitec to release mutant mosquitoes into the wild for the purpose of disease control.