By Tom Polansek and Heather Schlitz
KERRVILLE, Texas, July 23 (Reuters) - At a U.S.-funded facility in Panama, scientists are preparing to launch the first outdoor tests of genetically modified screwworm flies, a milestone in efforts to develop a more effective weapon against the flesh-eating parasite that has spread through Central America and into the United States.
Researchers said they will keep the flies confined in mesh cages, exposed to Panama's heat and humidity, to measure how long they survive
outside laboratory conditions before moving to later stages of field testing.
The Trump administration has touted the development of the genetically modified fly, called NovoFly, as a game-changer in the fight against New World screwworm. Widespread infestations could cause estimated losses of more than $1 billion to Texas' livestock industry and spread to other U.S. states.
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.
For decades, the most effective tool against them was 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 that 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 marching north into Central America and North America.
But now wild screwworm flies have spread throughout Mexico and in June infested livestock on Texas farms for the first time in decades. With cases spread over a large area, the sterile flies produced in Panama are not nearly enough to eradicate the parasite. The facility is operating at maximum capacity, but experts say 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.
Enter NovoFly, a screwworm fly that 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 screwworm population progressively decline until it is eradicated. The USDA started using the technique in 1957 to fight the pest, which was eradicated from the United States in 1966, and also used it to eliminate later outbreaks.
The NovoFly project is designed to boost the production of sterile flies. Currently, the Panama facility produces males and females. The females are useless in controlling the wild population, but there's no easy way to separate them, according to the USDA and entomologists.
"It's going to allow us to almost instantaneously double the number of sterile flies that we put in the fight," Scott Hutchins, USDA's chief scientist and an undersecretary, said of NovoFly at a news conference in June. "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.
Officials at the Kerrville lab told Reuters on an exclusive tour that 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 (COPEG), which operates the Panama plant, deferred requests for information to the USDA. The Panamanian Food Agency declined to comment.
SUCCESS NOT GUARANTEED
The outdoor testing is critical to determining the potential effectiveness of the NovoFly. Scientists do not know whether it will have the strength and virility to fly far enough to find and attract wild mates.
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, he said.
Field tests typically run for about six to eight weeks, said Maxwell Scott, an entomologist at North Carolina State University who helped develop NovoFly, warning that success was not guaranteed: "We may get out in the field, and it may not fly very well."
If NovoFly performs well in trials, it would take time to scale up production, according to the USDA. Rather than producing NovoFly initially in Panama, it may be less risky to do it at a new sterile-fly production facility expected to open in Texas late next year, experts said.
Adding NovoFly to the facility in Panama could risk disrupting the largest source of sterile flies and a collapse of production, if scientists fail to establish the correct diets, temperatures and conditions for the new strain.
"The last thing we'd want to do is rush a process to be able to have what's called a total brood collapse," said Rear Admiral Michael Schmoyer, who is leading USDA's efforts against screwworm, at a legislative hearing in Texas. "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.
Even a modest increase in the number of sterilized males could lead to a quicker eradication of wild screwworm flies, said Edwin Burgess, an assistant professor of veterinary entomology at the University of Florida who is not involved in the project. However, researchers need to make sure NovoFly is competitive against wild male screwworm flies for mating and can be reared successfully on a large scale, he said.
"There are still a lot of things that need to be done to get that technology to where it needs to be," Burgess said. "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.
Kerrville lab director Kim Lohmeyer 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 is 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."
(Reporting by Tom Polansek in Chicago and Heather Schlitz in Kerrville, Texas. Additional reporting by Adriana Barrera and Cassandra Garrison in Mexico City and Elida Moreno in Panama City. Editing by Emily Schmall and Claudia Parsons.)
