Genetically engineered mosquitoes—750 million of them—will be released in the Florida Keys in 2021 and 2022. The pilot program, which was approved for “experimental use” by the Environmental Protection Agency (EPA) in May, will test to see if genetically engineered mosquitoes are a good pest control alternative to spraying insecticides.


The specific target is the Aedes aegypti mosquito, which can carry serious, potentially lethal diseases like the Zika virusdengue, chikungunya, and yellow fever. The Florida Keys is currently dealing with an outbreak of dengue; 47 people have been infected so far this year, according to the Miami Herald.


But not everyone in the Florida Keys is thrilled about adding more mosquitoes into the area. Several residents and environmental advocacy groups have protested the plan. “The administration has used tax dollars and government resources for a Jurassic Park experiment,” Jaydee Hanson, policy director for the International Center for Technology Assessment and Center for Food Safety, said in a statement. “What could possibly go wrong? We don’t know, because EPA unlawfully refused to seriously analyze environmental risks, now without further review of the risks, the experiment can proceed.”


Some are even concerned that these genetically modified mosquitoes could end up creating wild hybrid mosquitoes that might increase the number of mosquito-borne illnesses in South Florida. There is precedent for that: One study, published in the journal Nature in 2019, details how these same genetically modified mosquitoes created a hybrid strain of mosquitoes, although the study’s authors says it’s “unclear” how this can impact the transmission of mosquito-borne diseases or efforts to control these mutant mosquitoes.


But Chad Huff, a spokesperson for the Florida Keys Mosquito Control District, tells Health that something needs to be done. “Aedes aegypti is becoming more and more resistant to pesticides applied by Florida Keys Mosquito Control,” he says. “It is extremely important that this organization explore other options for controlling this very dangerous mosquito that has made a lot of our local residents very sick.”


All of that said, it’s understandable that people have a few—or a ton of—questions about genetically modified mosquitoes. Here’s what you need to know.


What are genetically modified mosquitoes, exactly?

These mosquitoes were created by a company called Oxitec, and they will be released into the wild through “field tests,” the company says in a press release.


These particular mosquitoes are male, and they’re genetically modified to carry a protein that will “inhibit the survival of their female offspring when they mate with wild female mosquitoes,” Oxitec says. The male offspring will survive, though.


Mosquito fun fact: Only female mosquitoes bite people—the males eat flower nectar, Eva Buckner, PhD, a medical entomology extension specialist at the University of Florida, tells Health.


One thing Oxitec notes is that, since they’re only releasing male mosquitoes, they won’t bite and “will not pose a risk to people.” The company states: “it is also anticipated that there would be no adverse effects to animals such as bats and fish in the environment.”


This method has already been used in Brazil and “led to a 95% reduction in the local Aedes aegypti mosquito population,” Buckner says. “The efficacy of this technology has been demonstrated in prior small field trials,” she adds.


The World Health Organization (WHO) has weighed in on genetically modified mosquitoes as a method of mosquito control and calls it a “safe and potentially effective way” of reducing wild mosquito populations.


How will the genetically engineered mosquitoes be released?

To unleash these mosquitoes into the wild, boxes that contain millions of the genetically altered male eggs will be put somewhere in the Florida Keys. Water is added, Oxitec says, and the male mosquitoes will hatch and join the Aedes aegypti mosquito population in the area.


From there, they’ll mate with wild female mosquitoes and effectively kill off their female offspring. The male offspring will survive and carry genetic modification. “This process will continue generation after generation, ultimately leading to a reduction in the mosquito population,” Buckner says.


How can these mosquitoes help public health?

Given that mosquitoes can carry diseases that can make people sick or even be deadly, the hope is that these genetically modified mosquitoes will kill or greatly tamp down on the local mosquito population, taking these mosquito-borne diseases with it. “Being able to reduce the Florida Keys’ Aedes aegypti population is incredibly important,” Buckner says.


But Buckner adds that the use of genetically modified mosquitoes isn’t perfect. “Is this the silver bullet of mosquito control? Absolutely not,” she says. “The release of genetically modified mosquitoes is intended to be used as a part of an integrated mosquito control program, in which multiple methods of mosquito control are used at the same time.”