REDFIELD, Iowa (DTN) -- The U.S.-Mexico border opened yesterday to cattle imports through the Port of Entry at Douglas, Arizona.

The phased reopening was announced by USDA on July 24 for this week's trade through Arizona, to be followed by steps to open ports of entry at Santa Teresa, New Mexico, and Columbus, New Mexico. Those ports have been closed since May 2025 due to the spread of New World screwworm (NWS) northward through Mexico.

SAFEGUARDS, SCIENCE GUIDE RISK-BASED REOPENING

USDA said this risk-based plan will have several safeguards in place to ensure all animals entering the U.S. are free of NWS. Currently, only 46 NWS cases have been detected in the U.S., with the most recent being on August 16, in sheep located in Val Verde County, Texas, along the border. The first case of NWS in the U.S. was detected on June 3, 2026.

Texas and Southwestern Cattle Raisers Association President Stephen Diebel said in a statement, "Our members need continuity in commerce, but they also need confidence that every reasonable safeguard is in place to reduce the risk of New World screwworm. We support USDA's phased reopening based on its science and modeling and the months of work by USDA, state partners and producers."

Diebel continued that it expects USDA to close the ports if any trigger falls, as the priority remains protecting the U.S. cattle herd and wildlife while allowing cattle raisers and markets to operate normally.

MEXICAN CATTLE EXPECTATIONS

Oklahoma State University Extension livestock marketing specialist Derrell Peel said there is a lot of speculation about the reopening by both the U.S. and Mexico about how many cattle and of what size, as well as how fast they will come across the border.

Peel explained the number of head coming to the U.S. from Mexico has varied through the years, but on average was 1.17 million head per year for the 20 years from 2004 to 2023. "On average, 36% of annual Mexican cattle imports cross from September through December," he said. "Based on history, it might be possible for 90,000-100,000 head of cattle to cross at the Douglas port in the last four months of the year. It will likely take several weeks for ports to return to full capacity."

For the remainder of 2026, Peel expects the number of Mexican cattle coming across the border to the U.S. could be as many as 250,000 but is more likely to be about 150,000 head.

STERILE FLIES LEAD THE FIGHT AGAINST NWS

The main combat against the NWS is the release of sterile flies. USDA's Agricultural Research Service (ARS) researchers have been working on the development of the NovoFly screwworm strain to be used as well.

"Releasing sterile screwworm flies is a proven, decades-old approach to eliminating populations of this pest and preventing the harm it inflicts--physically to livestock animals and wildlife and financially to the producers who raise livestock for our milk, meat, hide and other products," said Kim Lohmeyer, Director of ARS's Knipling-Bushland U.S. Livestock Insects Research Laboratory in Kerrville, Texas. "Advances in genetics have now given us better tools to understand the screwworm's population dynamics and leverage that knowledge for improved control methods, including sterile fly releases."

The NovoFly is an all-male strain of the screwworm fly that can be produced twice as many, doubling the number available for releases in hopes of moving toward eradication more quickly. These sterile male flies would then mate with wild female flies. The result is eggs that fail to hatch, thus helping collapse the NWS population.

The NovoFly is engineered with a genetic "switch" that kills female larvae during early rearing stages but doesn't function in males. This allows for doubling the number of males that can be brought to maturity for release using the same amount of artificial diet and equipment, according to ARS.

The NovoFly is currently undergoing regulatory approval before the Environmental Protection Agency. This, along with the sterile fly production facilities in Panama, Mexico, and the opening of a new facility in south Texas, will help combat the pest back south of the Darien Gap.

USDA's website with all information about NWS is https://www.aphis.usda.gov/…

**

Editor's Note:

For more DTN coverage of the New World screwworm threat and the response by the government and livestock industry, visit our Spotlight on New World Screwworm page at https://www.dtnpf.com/…

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

Follow her on social platform X @JennCattleGal

(c) Copyright 2026 DTN, LLC. All rights reserved.