REDFIELD, Iowa (DTN) -- USDA's Animal and Plant Health Inspection Service (APHIS) has shifted sterile New World screwworm (NWS) fly release to include into Texas to help efforts to stop the northern spread of the pest.

In an APHIS news release late Friday, APHIS stated the new dispersal area, or polygon, will include operations about 50 miles into Texas, along the U.S. border with the state of Tamaulipas, Mexico, where 100 million sterile flies will be released per week. Strong surveillance will continue along the border and in Texas as well.

"At Secretary (Brooke) Rollins' direction, our highest priority is protecting the United States from screwworm," Dudley Hoskins, under secretary of Marketing and Regulatory Programs for USDA said in the Friday statement. "The northernmost active case of NWS in Mexico is still about 200 miles away from the border, but we've seen cases continue to spread in Tamaulipas and further south in Mexico, so we are proactively shifting our polygon as we make every effort to prevent NWS from reaching our border."

ARGENTINE HORSE QUARANTINED IN FLORIDA

The U.S. border has been closed to imports of Mexican cattle, bison and horses since July 2025.The USDA reported earlier this week the import protocols and requirements were used at an equine import quarantine facility in Florida where a horse from Argentina was examined and APHIS identified an open wound on the animal.

Upon further examination, larvae were found in the wound. The horse was treated with medication to kill any larvae. Samples were shipped to the National Veterinary Service Laboratory in Ames, Iowa, which confirmed they were NWS larvae. The animal has been contained at the facility and will be quarantined until officials confirm it is free of the pest.

DEFENSE EFFORTS RAMP UP

The recent Texas statewide disaster declaration will also help better equip the state for prevention efforts to keep NWS out. The declaration this week by Gov. Greg Abbott allows the Texas NWS Response Team to fully utilize all state government prevention and response resources to prevent the re-emergence of this destructive parasite. (See https://www.dtnpf.com/…)

The National Cattlemen's Beef Association thanked USDA for the continued diligence and swift, science-based action to protect the U.S. cattle herd from NWS. In a statement, NCBA commended the proactive action of releasing sterile flies along the border to help safeguard animal health.

R-CALF USA CEO Bill Bullard told DTN, "This is great news for U.S. livestock and wildlife. Secretary Rollins is demonstrating her absolute commitment to preventing this devastating pest from entering our country."

OLD TECHNIQUE STILL USED

The sterile insect technique has been used since it was first used in 1936 to fight NWS. The same technique is used in present day for eradication. The flies are sterilized using ionizing radiation prior to release. Since the flies only mate once, no offspring are produced, thus drastically reducing the wild NWS population. This, paired with surveillance, movement restrictions, education and outreach, should help control and eradicate NWS.

"USDA will continue to deploy its intensive NWS response efforts including implementing import protocols, ongoing surveillance and trapping efforts along the border, investing in NWS innovation, and supporting robust response activities in Mexico and Central America," the release said.

"Because it is important to continue ongoing surveillance efforts while releasing sterile insects, it is possible that sterile NWS flies could be caught and/or reported within Texas. To ensure officials can tell the difference between sterile and wild NWS flies, USDA will dye the sterile pupae, and the dye will transfer to the sterile flies when they hatch. The fluorescent dye will glow under UV light and may also be visible to the naked eye. If a sterile fly is captured in a trap, this dye will allow animal health officials to quickly rule the fly out as a threat," the USDA news release stated Friday.

Combating the threat of New World Screwworm remains a top priority for NCBA and its state affiliates, and expanding sterile fly production and dispersal, the most effective tool for eliminating screwworm, is a critical step forward. NCBA also stressed the importance of the construction of the sterile fly production and distribution facilities planned in Texas to help further protect the U.S. cattle herd with a more rapid response.

SURVEILLANCE PREVENTS PROBLEMS

The USDA continues to lead intense surveillance and monitoring along the U.S.-Mexico border. More than 120 NWS-specific traps are placed in high-risk areas in border states. Through the end of January, more than 42,000 flies have been captured, with no NWS detections. More than 9,300 wild animals of 39 different species have been inspected by APHIS Wildlife Services and no signs of NWS have been found.

USDA continues to ask U.S. animal owners to check their pets and livestock for signs of NWS and report anything suspicious to their state animal health officials, USDA area vets and local veterinarians.

Adult screwworm flies are about the size of a common housefly with metallic green or blue body, orange eyes, and three dark stripes down the back. The maggots infect living warm-blooded animals. These animals, including humans, will need medical attention immediately.

Also see:

-- "USDA Launches $100M Screwworm Challenge," https://www.dtnpf.com/…

https://www.aphis.usda.gov/…

-- NWS status from USDA: https://www.dtnpf.com/…

Jennifer Carrico can be reached at jennifer.carrico@dtn.com

Follow her on social platform X @JennCattleGal

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