U.S. Deploys 'Glowing' Sterile Flies as Buffer Against Flesh-Eating Screwworm Threat at Mexican Border

By Tom Polansek, with additional reporting

CHICAGO, Feb 2 (Reuters) – The U.S. Department of Agriculture (USDA) is launching an aerial counteroffensive against a resurgent livestock menace, deploying sterile flies marked with glow-in-the-dark dye along the U.S.-Mexico border and into southern Texas. The urgent move aims to halt the northward spread of the New World screwworm, a flesh-eating parasite causing infestations in Mexican cattle and threatening the U.S. livestock industry.

The screwworm, a parasitic fly, poses a gruesome threat. Females lay eggs in open wounds of warm-blooded animals. Upon hatching, larvae burrow into living tissue, causing severe damage or death if untreated. The USDA has already suspended imports of Mexican livestock to prevent the pest's entry, exacerbating a domestic cattle shortage that has driven consumer beef prices to historic highs.

For decades, the USDA has waged a successful sterile insect technique (SIT) campaign, producing over 100 million sterile male flies weekly at a Panama facility and releasing them over Central America to disrupt reproduction. Now, the frontline is shifting north. Following 20 confirmed infestations since late December in the Mexican state of Tamaulipas—which borders Texas—the agency will establish a "buffer zone" by dispersing sterile flies north of the outbreak epicenter.

"Given the proximity to Texas and the national herd, this preemptive action is not just advisable—it's essential," said Dr. Sonja Swiger, an entomologist at Texas A&M University.

Officials acknowledge the current sterile fly production is insufficient to eradicate the pest in Mexico. A planned Texas production facility is at least a year from operation, prompting the USDA to commit up to $100 million to scale up output. For now, the new dispersal operations will extend approximately 50 miles into Texas along the Tamaulipas border.

"Our highest priority is protecting the United States from screwworm," stated USDA Under Secretary Dudley Hoskins, noting the northernmost Mexican case remains about 200 miles from the border.

The sterile flies will be dusted with a fluorescent dye, making them visible under UV light—a tactic to help researchers monitor the program's reach and distinguish them from wild, fertile pests. The U.S. strategy aligns with technical proposals Mexico has advanced since last November, according to a Mexican government statement.

This modern effort echoes the mid-20th century campaign that eradicated screwworms from the U.S. using aircraft to drop cardboard boxes of sterile insects over outbreak zones. "The technique remains highly effective, provided you can overwhelm the wild population," explained Dr. Max Scott, an entomology professor at North Carolina State University.

Experts warn the Tamaulipas outbreaks suggest a local fly population is becoming established, beyond mere transmission via transported animals. While unseasonably cold Texas weather may temporarily slow the pest's advance, the economic toll is already being felt. "Our beef segment continues to face significant margin pressure due to tight cattle supplies," said Devin Cole, COO of Tyson Foods, on a recent earnings call, adding there is no clarity on when the import ban might lift.

Voices from the Ground

Maria Gonzalez, Rancher, Laredo, Texas: "Seeing those planes release flies is surreal, but if it keeps my herd safe, I'm for it. We've already lost enough from the trade halt."

Dr. Arjun Patel, Veterinary Epidemiologist, University of Arizona: "This is a prudent, science-driven response. The buffer zone is a classic epidemiological firewall. The real test will be sustaining the sterile fly output long-term."

Rick Carlson, Feedlot Owner, Kansas: "It's a band-aid on a bullet wound. The government dithered until it was at our doorstep. Now we're stuck with sky-high prices and a bug problem that should've been contained years ago. Where's the long-term plan?"

Professor Elena Ruiz, Agricultural Policy, UC Davis: "This situation underscores the fragility of integrated North American food systems. A pest outbreak in one nation quickly becomes a supply chain and inflation issue for all."