This week, mosquito eggs placed in the Florida Keys are expected to hatch tens of thousands of genetically modified mosquitoes, a result of the first U.S. release of such insects in the wild. A biotechnology firm called Oxitec delivered the eggs in late April as part of a federally approved experiment to study the use of genetic engineering—rather than insecticides—to control disease-carrying mosquito populations. The move targets an invasive species, called Aedes aegypti, that carries Zika, dengue, chikungunya, yellow fever and other potentially deadly diseases, some of which are on the rise in Florida.
The experiment relies on a genetic alteration that will be lethal to a large number of future offspring. In this case, male mosquitoes have been modified to carry a gene that makes their female progeny dependent on the antibiotic tetracycline—and thus fated to die in the wild. As the mating cycle repeats over generations, female numbers are depleted, and the population is suppressed. The modified insects eventually die off, making this approach self-limiting.
Oxitec overcame significant regulatory hurdles before getting the go-ahead from the U.S. Food and Drug Administration in 2016 and then the Environmental Protection Agency in 2020. If the current pilot effort is successful, the firm is set to release as many as 20 million more males in the prime of Florida’s mosquito season later this year. The results of the experiment could ultimately help address concerns about releasing genetically modified organisms into the wild.
To learn more about the risks and rewards of Florida’s foray into bioengineered pest control, Scientific American spoke with Omar Akbari, a molecular biologist whose lab works on genetic control technologies at the University of California, San Diego. He is also a co-founder of Agragene, a biotech company that is using genetically engineered agricultural pests as a biological pest control.[An edited transcript of the interview follows.]
Do you think the Aedes aegypti experiment in the Florida Keys will reduce the spread of mosquito-borne diseases?
The current method of controlling this species is to use insecticides, but they don’t really work well. We’ve noticed resistance in the field, so new technologies are definitely needed.
Oxitec’s technology for releasing genetically modified insects has been tested in other places. [The company has] reported reaching A. aegypti population suppression of more than 90 percent in many of their releases, including effective control of the A. aegypti population in Brazil. Given its prior testing, the experiment in the Keys is likely to work and to suppress A. aegypti populations. And hopefully it will directly translate into an epidemiological impact, effectively reducing disease transmission.
How safe is this technology?
It’s extremely safe. The EPA has done its due diligence and tested many of the potential side effects of this technology. The real question here is: What are the existing control mechanisms that are in place? This mosquito has been controlled using many different broad-spectrum insecticides in Florida, including pyrethroids that also kill honeybees, ladybugs, dragonflies and other insects. Pictures show aerial spraying of insecticides from airplanes over neighborhoods in Florida during the Zika virus outbreak in 2016. By comparison, Oxitec’s technology is extremely safe. It’s only going to target A. aegypti, and you’re using the mosquito to control the mosquito.
Is there a risk to the ecosystem?
It’s a misconception that this process could get rid of all mosquitoes. There are more than 3,500 different species of mosquitoes on earth. A handful of them transmit pathogens. 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. 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.
Do you anticipate the future use of Oxitec’s technology in other U.S. states?
Right now it is only approved to do mosquito egg releases in that one area of Florida. It’s authorized here for experimental use. And the technology is localized. These mosquitoes can’t travel very far.
The first requirement for use of the technology in other areas will be success with the current experiment in Florida. Once that is in hand, Oxitec can apply for more permits to do broader releases in other areas. If that were to happen, the process would resemble what took place in Florida. I think [Oxitec] would connect with the local mosquito-control districts in those locations and coordinate releases and monitoring the density of the A. aegypti female population over time. Getting approval in other locations might also require putting it on a ballot to get the public to weigh in on the decision, as was done in Florida.
What are the possible limitations of this approach to controlling mosquitoes that spread diseases?
One question is scalability. Can they scale this technology to eliminate this pest from, let’s say, all the states in America that it’s present in, which is basically half of the U.S.? Or is it only useful in small communities? And if they scale if it, what is the cost associated with that?
Also, species-specific technology is a double-edged sword. On the one hand, you’re only targeting one species. On the other hand, there are often multiple species transmitting a pathogen. For example, in Brazil, you have two different species that transmit dengue virus—A. aegypti and Aedes albopictus. That’s also the case in Florida. So if you get rid of one of them, the other is still out there.
With global warming, how likely is it that other regions will take the same course that the Florida Keys mosquito district has?
Some already have. Oxitec has received approvals to do releases of its modified A. aegypti mosquitoes in the Cayman Islands and Panama. It is doing trials in India—genetically modified mosquitoes are released into cages with wild-type mosquitoes to mate and then compared with cages without the modified insect. [Others have] done releases in Malaysia and Australia. And as there are more examples of success stories, I think more countries will be willing to adopt this technology, assuming that the costs make sense.
With global warming, the habitable range of A. aegypti mosquitoes is expanding. The species now is present in many U.S. states, whereas 10 years ago it wasn’t. This, too, is going to become more important as this mosquito species becomes more prevalent and the pathogens also become more prevalent.
What biological pest-control technologies are you currently working on?
Our lab has a [preprint] paper currently under review describing a new CRISPR-based technology that can be used to eliminate A. aegypti populations. It’s also self-limiting. We’re excited about this because we were able to eliminate the populations in experimental cages in the lab. And we think this technology might be a next-generation technology that can be used alongside the Oxitec technology. The outcome is very similar.