Scientists at a U.S.-funded facility in Panama are preparing to launch the first outdoor tests of genetically modified screwworm flies, a critical step in protecting American ranchers from a flesh-eating parasite that threatens more than $1 billion in losses to Texas' livestock industry alone. Researchers will keep the flies confined in mesh cages and expose them to Panama's heat and humidity to measure survival rates before advancing to later field testing stages.
The Trump administration has championed the genetically modified fly, called NovoFly, as a game-changer in the fight against New World screwworm. Wild screwworm flies have now spread throughout Mexico and in June infested livestock on Texas farms for the first time in decades. Screwworms are parasitic flies whose females lay eggs in open wounds and mucous membranes on any warm-blooded animal. Once the eggs hatch, hundreds of screwworm larvae use their sharp mouths to burrow through living flesh, eventually killing their host if left untreated.
The Current Defense
For decades, the most effective tool against them has been widespread dispersal of sterile screwworm flies, which are now mostly produced at the facility in Panama. The U.S. Department of Agriculture and Panama's Ministry of Agricultural Development jointly manage and finance the plant, which produces about 100 million sterile flies per week. Opened in 2006 on the narrow isthmus, the plant was intended to maintain a barrier to stop wild screwworm flies from moving north into Central America and North America.
With cases spread over a large area, the sterile flies produced in Panama aren't nearly enough to eradicate the parasite. Experts said they need 500 million a week to push screwworm flies back to the geographic boundary of the Darien Gap, the stretch of rainforest between Panama and Colombia.
The NovoFly Solution
NovoFly is genetically engineered to produce only males. Once the male offspring are sterilized, they could be released to mate with wild female screwworm flies, which then lay unfertilized eggs. Wild female screwworm flies normally mate only once, so sterile male flies can make the population progressively decline until it's eradicated. The USDA started using the technique in 1957 to fight the pest, which was eradicated from the United States in 1966, and later used it to eliminate other outbreaks.
The NovoFly project is designed to boost the production of sterile flies. The Panama facility currently produces males and females, and the females are useless in controlling the wild population, but there's no easy way to separate them, according to the USDA and entomologists.
Scott Hutchins, USDA's chief scientist and an undersecretary, said at a news conference in June, "It's going to allow us to almost instantaneously double the number of sterile flies that we put in the fight," and, "It's going to give us a tremendous edge."
The USDA conducts some of its screwworm research at the Knipling-Bushland U.S. Livestock Insects Research Laboratory in Kerrville, Texas, a facility named after American entomologists who developed the process to sterilize screwworm flies. The flies are blasted with radiation before release, a process that would also be used on NovoFly.
Field Testing Timeline
Officials at the Kerrville lab said scientists were expecting approval soon from Panama's biosecurity agency to begin NovoFly tests outdoors at the Panama lab. The Panama-United States Commission for the Eradication and Prevention of Screwworm, which operates the Panama plant, deferred requests for information to the USDA, and the Panamanian Food Agency declined to comment.
After the initial tests in Panama, larger field trials on NovoFly are expected to begin at a ranch nearby in nine to 12 weeks, when researchers will release 50,000 of the insects every few days, said Alex Arp, a USDA research geneticist working in Panama. The flies will be marked with fluorescent dyes visible under black light, and traps around the ranch will allow researchers to track how long each release survives.
Maxwell Scott, an entomologist at North Carolina State University who helped develop NovoFly, said field tests typically run for about six to eight weeks and warned, "We may get out in the field, and it may not fly very well."
Production Challenges
If NovoFly performs well in trials, it would take time to scale up production. Experts said it may be less risky to produce it at a new sterile-fly production facility expected to open in Texas late next year rather than initially in Panama. Adding NovoFly to the Panama facility could risk disrupting the largest source of sterile flies and cause a collapse of production if scientists fail to establish the correct diets, temperatures and conditions for the new strain.
Rear Admiral Michael Schmoyer, who is leading USDA's efforts against screwworm, said at a legislative hearing in Texas, "The last thing we'd want to do is rush a process to be able to have what's called a total brood collapse," and, "You start with zero, and then you have to build up again."
The U.S. Environmental Protection Agency published a proposed decision to register NovoFly in June, according to the USDA. If fully approved, NovoFly would become the first genetically modified insect to get full EPA clearance, Scott said.
Edwin Burgess, an assistant professor of veterinary entomology at the University of Florida who isn't involved in the project, said even a modest increase in the number of sterilized males could lead to a quicker eradication of wild screwworm flies. He said researchers need to make sure NovoFly is competitive against wild male screwworm flies for mating and can be reared successfully on a large scale. Burgess said, "There are still a lot of things that need to be done to get that technology to where it needs to be. But it's certainly very, very promising."
Mexico supports using the male-only flies and could be producing them by the end of the year at a newly reopened production plant, said Gabriel Ayala, head of animal health for Mexico's National Service for Agri-Food Health, Safety and Quality. Eventually, they could be produced in Panama, Mexico and at the planned U.S. plant in Texas, he said.
Kim Lohmeyer, Kerrville lab director, said she hopes the U.S. can eradicate screwworms much faster than the decades it took before the pests were controlled in the 1960s. But even if the NovoFly trials succeed and it's brought into production, it will likely take more than a year to control the pest, she said. "It will take some time and effort," she said. "We need more flies."
Why This Matters:
The screwworm outbreak represents a direct threat to American agriculture and food security, with potential losses exceeding $1 billion to Texas ranchers alone if the parasite spreads unchecked. The decades-old sterile fly program, while effective, can't produce enough insects to meet current demand—a production gap that leaves livestock vulnerable and threatens to spread the infestation beyond Texas. NovoFly offers a market-driven innovation that doubles production capacity by eliminating wasteful female fly production, demonstrating how targeted scientific advancement can solve problems government programs alone can't address at scale. The cautious rollout at a new Texas facility rather than risking Panama's existing production shows prudent risk management. If approved, this would mark the first genetically modified insect to receive full EPA clearance, potentially opening pathways for similar agricultural innovations. Success depends on proving the technology works in real-world conditions and scaling production across multiple facilities—a timeline measured in years, not months, underscoring the long-term investment required to protect American ranchers.