Nuclear methods for screwworm eradication

Last week, the International Atomic Energy Agency announced the launch of a coordinated research project focused on a nuclear technique that can tackle the reemergence of New World screwworm (NWS) in Central America, Mexico, and the United States.

The NWS (Cochliomyia hominivorax) is a parasitic fly that lays eggs in mammal wounds, causing severe lesions when the eggs hatch and the larvae begin feeding on living tissue. The NWS was eradicated from the southwestern United States in 1966, from Mexico in 1991, and all the way south to Panama in 2006.

The sterile insect technique (SIT) was critical to eradication efforts. SIT suppresses the screwworm fly population by introducing large quantities of sterilized flies to the environment. A sterile insect barrier was set up in the Darién Gap in southern Panama, effectively keeping the screwworm fly out of the eradicated area for nearly two decades.

Since 2023, outbreaks have been occurring in Central America and Mexico, spreading northward. According to the Centers for Disease Control and Prevention, as of June 8, 2026, Mexico and Central America have had more than 185,000 cumulative reported cases of NWS in animals and more than 2,100 reported cases in people.

"The return of New World screwworm is already causing serious damage in the region, threatening animals, livelihoods, and economies," said IAEA Director General Rafael Mariano Grossi.

On June 3, the U.S. Department of Agriculture (USDA) confirmed a report of an animal infested by the screwworm fly in Texas, the first U.S. animal case of NWS in more than 40 years-and more cases have followed.

Early detection of the NWS and rapid response is essential. In the summer, the flies attempt to spread northward and can travel 50-100 miles per generation. Beyond this, the screwworm fly can spread through the transportation of infested hosts. To prevent this, the USDA has suspended imports of live cattle, bison, and equids from Mexico. It is also establishing quarantines, movement controls, and surveillance within 20 kilometers of identified infested zones.

More about NWS: The NWS can infect wounds as small as a tick bite, and common sites include dehorning or castration wounds, shearing nicks, and identification methods such as notches or tagging sites. When a screwworm fly lays its eggs, it takes just 10-12 hours before those eggs hatch into the larvae stage.

"That early instar stage of the larvae is very tiny and most of the time will be unrecognizable by most humans because of its small size and the fact that we're just not familiar with searching for these," said Sonja Swiger, a professor at Texas A&M University who teaches a New World Screwworm Preparedness and Response Education course. "A lot of times those little larvae will also be under the skin, inside the wound, eating on that flesh, but again, they're so small they do go unnoticed."

Over five to seven days, the larvae feed constantly and grow rapidly. Left untreated, the infestation can cause bacterial infection or even death within 7-14 days, making it a devastating pest to livestock and wildlife, even occasionally infesting humans. Swiger said newborn animals are particularly susceptible. The newborn navel is a common infestation site, and once infested, newborns have a near-100 percent fatality rate.

According to the IAEA, changing weather patterns, globalization, and unlawful transboundary animal movements have all contributed to the recent screwworm fly spread. Now, the USDA is once again relying on SIT to eradicate the pest.

How SIT works: SIT has a counterintuitive starting point: breeding more screwworm flies. These mass-reared insects are sterilized and then released into the wild, where they will mate but only lay unfertilized eggs.

SIT is highly effective against the NWS in part due to its breeding habits: Female screwworm flies mate only once in their lifetime, so a female fly that pairs with a sterile male will never produce any offspring.

According to the IAEA, SIT is "among the most environment-friendly insect pest control methods ever developed."

It does not rely on chemical pesticides, and it singularly targets the species being controlled. SIT-sterilized insects are safe for predators to eat.

Sterile fly production plants have been set up to facilitate the eradication of the NWS in infested areas. These facilities irradiate NWS pupae, damaging DNA in the flies' reproductive cells, making them infertile.

SIT irradiators fall into two categories: gamma rays from radioactive isotopes and beams generated electrically by particle accelerators.

Exposing densely packed canisters of pupae to the high-energy photons emitted by colbalt-60 has historically been the primary irradiation method. It can reliably provide a uniform radiation dose, but with a 5.3-year half-life, it requires regular replenishment.

Cesium-137 is functionally equivalent to Co-60 for SIT, with the benefit of a 30-year half-life, but its soluble-powder form makes it a higher security risk, causing it to be largely phased out.

X-ray or electron beams can also be used to sterilize insects. These methods lack the security risks, regulatory hurdles, and required periodic replenishments involved in using a radioactive source.

However, X-ray methods create lower, mixed-energy photons that penetrate a dense canister less evenly. Electron beam methods only offer shallow penetration, requiring pupae to be irradiated in thin, even layers.

Accelerator-driven SIT methods are an area of active research. In 2025, the National Nuclear Security Administration announced a partnership with Texas A&M University to advance SIT using electron beam technology.

The sterilized insects are released in infested areas, mostly in chambers that are dispersed by aircraft, suppressing the population. SIT does not impact the insect's flying abilities, longevity, searching behavior, or mating abilities. The USDA aims to target the release of sterilized flies in regions where active cases have been confirmed.

SIT is best known for its use in combatting screwworm flies, but it has also been applied to other types of insects, including mosquitos in Florida and Cuba.

Current SIT efforts: The IAEA said it could take up to 600 million sterile flies per week to control the current outbreak. According to the Panama-United States Commission for the Eradication and Prevention of Screwworm from Cattle (COPEG), its SIT facility in the Panama is operating at capacity, producing around 100 million sterile flies per week.

Efforts are also underway to increase capacity across Mexico and Central America, and in April, the USDA announced it had broken ground on a production facility in Texas. According to the announcement, the facility is targeted to begin producing 100 million sterile flies per week by November 2027, eventually scaling up to 300 million per week. This facility will use Co-60 irradiators.

"USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico. The United States has defeated this pest before, and we will do it again," said Dudley Hoskins, undersecretary for marketing and regulatory programs at the USDA.

The IAEA CRP: According to the IAEA, it is launching a new coordinated research project that will bring together experts from more than 20 affected countries to strengthen surveillance and control methods, improve mass-rearing and sterilization, study mating compatibility and competitiveness, and support the release of sterile flies. The five-year project has a planned budget of $1 million.

"To meet the needs of greater numbers of sterile flies, the project will bring together expertise to improve the cost-effectiveness of mass-rearing, developing, and managing screwworm strains, enhancing handling and release methods and studying mating behavior and competitiveness," said Rui Cardoso Pereira, head of the IAEA Insect Pest Control Section.

More resources: The USDA has a dashboard tracking NWS confirmed detections in Mexico and the United States, which it updates daily.

The Texas Division of Emergency Management has a webpage covering how to spot NWS, sample collection procedures, and offers a free NWS preparedness and response education online course.