AINEWS
USDA's screwworm playbook worked. The next U.S. farm threat has no script.
The New World screwworm, a flesh eating livestock parasite eradicated from the U.S. in 1966, has returned to Texas and New Mexico.
The New World screwworm, a flesh eating livestock parasite eradicated from the U.S. in 1966, has returned to Texas and New Mexico.
The U.S. Department of Agriculture confirmed on June 3, 2026, that a flesh-eating livestock parasite called the New World screwworm had been detected in a three-week-old calf in Zavala County, Texas. Within roughly three weeks, the parasite had been found in 9 Texas counties and southeastern New Mexico, with 16 affected premises and 18 counties now under quarantine.
That was supposed to be the easy threat.
The New World screwworm is a fly whose larvae burrow into the wounds of warm-blooded animals and often kill them. The U.S. eradicated the species in 1966 using a sterile-insect technique, flooding infested areas with sterilized male flies so wild females cannot reproduce. For six decades, USDA has kept the species contained to South America, Panama, and parts of the Caribbean. When the fly started creeping north through Central America in 2023 and crossed into Mexico, a RAND research team predicted it would eventually reach the U.S. The system bought itself time. It did not use that time to keep the fly out.
Now the response is unfolding exactly as rehearsed. USDA has imposed a 20-kilometer infested-zone quarantine, intensified trapping and wildlife surveillance, and resumed aerial sterile-fly releases at roughly 4 million flies per week. A new ground dispersal facility at Moore Air Base in Edinburg, Texas, activated in February, handles fluorescent-dyed sterile pupae so field biologists can confirm that released insects are doing their job.
For a rancher in the Hill Country, that is reassurance. For a biosecurity researcher, it is the wrong kind of reassurance.
"The U.S. has contained this outbreak using a known and practiced technique," a team of researchers led by RAND's Christopher Hoard wrote in a June 2026 commentary. "But the broader U.S. agricultural biosecurity system is poorly prepared for the next threat, which may not come with a 60-year-old playbook."
The companion research report, Agricultural Security Considerations for the U.S. Corn Belt, lays out the larger case. The corn crop that underpins U.S. ethanol, livestock feed, and export markets is more genetically concentrated than it was in 1970, when a single fungal epidemic destroyed about 16% of the U.S. corn harvest. The 1970 Southern corn leaf blight hit because almost every hybrid planted that year carried a single genetic vulnerability called Texas male-sterile cytoplasm that made the crop uniformly susceptible. Adjusted for inflation, the epidemic cost the equivalent of roughly $8 billion in losses. The industry diversified afterward. Concentrations have rebuilt since.
The same logic applies to deliberately introduced threats. In 1978, Israeli citrus exporters discovered that Jaffa oranges had been injected with mercury to scare foreign buyers off Israeli produce. A decade later, the 1989 Chilean grape cyanide scare triggered a U.S. import ban and an industry loss estimated around $330 million, and a near-permanent shift in how food-safety agencies think about intentional contamination. These were not fictional scenarios. They were tested, low-tech attacks on agricultural supply chains.
The RAND team identifies three structural changes that could close the gap. Expand pathogen surveillance into agriculture the way public health already monitors human disease. Today, USDA tracks a small list of named livestock pests. A corn or soybean pathogen that has never appeared in the U.S. is, by definition, off the radar. Fund field-deployable crop biosensors and AI-assisted screening at border crossings and grain elevators. The technology exists in laboratories. It does not yet exist at the ports where bulk grain actually moves. Give USDA a rapid-response research funding mechanism modeled on the National Science Foundation's RAPID grants, which can move small sums to researchers within days when an unexpected event demands investigation. Today, an agricultural emergency waits on a normal appropriations cycle.
The screwworm story will not end with the screwworm. As Hoard and colleagues noted, the barrier ultimately failed — the northward spread was first documented at a checkpoint in November 2024, and by June 2026 the U.S. had confirmed detections. Each week of confirmed detection on the USDA dashboard is another week the U.S. has spent extending the old playbook rather than building the new one. The harder test, the one with no sterile-fly workaround, is still in the queue.