Rollins Warns Mexico Over Screwworm

WASHINGTON (DTN) -- Agriculture Secretary Brooke Rollins is pressing Mexican authorities to allow more unfettered access to flight crews trying to eradicate the outbreak of New World Screwworm in southern Mexico, or the United States will again suspend imports of Mexican livestock.

In a letter Saturday to Mexican Secretary of Agriculture and Rural Development Julio Antonio Berdegue Sacristan, Rollins warned that the outbreak of New World Screwworm (NWS) "continues to expand in southern Mexico" and "we are now at a critical inflection point in our shared campaign against this pest, and I am very concerned about our collaboration."

In her letter, she listed the issues of concern and what the U.S. wants Mexico to do. "If these issues are not resolved by April 30, USDA will restrict the importation of animal commodities, which consist of live cattle, bison, and equine originating from or transiting Mexico to protect the interest of the agriculture industry in the United States," Rollins stated.

Mexican President Claudia Sheinbaum was asked about the warning from the U.S. at her regular morning press conference on Monday, Reuters reported.

"There are many control systems that already existed in Mexico, but now we are strengthening them, starting from the southern border, and throughout the entire country, to prevent the spread," she said, according to Reuters.

CRITICAL OF MEXICO

Rollins was critical of Mexico for not launching "full deployment of sterile insect technique" operations, which she stated "represents a lost opportunity to contain this pest and prevent its spread beyond the Isthmus of Tehuantepec in southern Mexico."

Essentially, Mexico has imposed restrictions on a USDA Animal and Plant Health Inspection Service (APHIS) contractor, Dynamic Aviation, from conducting "high-volume precision aerial releases" of sterile flies that USDA stated is needed to suppress and eliminate the NWS population.

"The inability of any more of these providers to operate fully comprises the integrity of our regional strategy," Rollins wrote to the Mexican Ag secretary.

LIMITED FLIGHTS AND OPERATIONS

Mexican authorities have limited Dynamic's flights under a 60-day permit. Mexico also has limited operations to six days a week instead of seven days. Mexican authorities also are "imposing substantial import duties on critical aviation parts, dispersal equipment, and sterile fly shipments," despite the fact that the entire operation is being funded by the U.S. government "to support our shared goal of stopping the northward spread of NWS and pushing the disease back toward the biological barrier of the Darien gap. The Darien gap is a 60-mile stretch of jungle between Central America and South America.

"We do not understand how our official efforts to stop a common pest can be subject to such burdensome custom duties," Rollins wrote in her letter.

WHAT U.S. WANTS FROM MEXICO

Rollins called on her counterpart to engage both customs and other relevant federal officials to help facilitate Dynamics' operations "for a minimum of one year, preferably as long as needed or indefinitely."

Rollins also called for clearance and a waiver of import duties for aircraft parts and the sterile flies, and for Mexico to designate a high-level point of contact in the Mexican government to work directly with APHIS.

Rollins noted, "Time is of the essence. Every delay in granting fully operational authority and eliminating customs barriers undermines our collective ability to carry out this emergency response."

Year-to-date, Mexico has exported more than 155,400 cattle to the U.S., the vast majority of which are feeder cattle. That's roughly 274,000 fewer cattle imports from Mexico compared to the first four months of 2024.

The U.S. had temporarily banned Mexican cattle imports on Nov. 22, 2024, but reopened the border to Mexican cattle on Feb. 1, 2025.

WHY NWS IS A CONCERN TO U.S.

New World Screwworm are fly larvae that infest living tissue of warm-blooded animals, causing infection. According to APHIS, these maggots will burrow into a wound, feeding as they go, doing extensive damage by tearing the host's tissue with sharp mouth hooks. The wound becomes larger and deeper. NWS can cause serious, even deadly damage to the animal.

Eradicating NWS is only possible through the sterile insect technique. Since the female fly only mates once, this helps eliminate the population.

The National Cattlemen's Beef Association and the Texas & Southwestern Cattle Raisers Association each commended Rollins for pressing Mexico on the issue.

"The U.S. spent millions of dollars to eradicate New World screwworm from our borders in the 1960s but unfortunately, we are now facing this dangerous threat again," said NCBA President and Nebraska cattleman Buck Wehrbein. "Screwworm is very destructive and could cost American producers millions of dollars a year if it reaches us. Americans have been investing in prevention efforts in Central America for decades, but we can't stop this without Mexico's participation. NCBA strongly supports Secretary Rollins holding Mexico to their commitments regarding screwworm eradication."

Carle Ray Polk Jr., president of the Texas & Southwestern Cattle Raisers, said Mexico has fallen short in its efforts to control NWS and is putting more burden and risk on the U.S.

"We continually advocate for proactive efforts to manage NWS before it reaches the U.S. border, and welcome the supportive consequences put in place by Secretary Rollins that can spur needed action to protect America's cattle industry, food supply and wildlife populations," Polk said.

Earlier in April, Texas & Southwestern Cattle Raisers Association had members travel to in Panama to see the world's only large-scale sterile fly production facility. This facility provides the sole defense against the spread of NWS across North and South America. Flies that came from this facility have inconsistently been denied access in certain parts of Mexico for dispersal flights.

"Mexico has tools at their fingertips, and to not allow aerial drops of sterile flies is irresponsible," Polk said. "Texas will be the first to face the consequences of their inaction, and cattle raisers need strong leadership from USDA like Rollins demonstrated today to push back against their failures."

Also see, "APHIS Expands Biological Barrier Into Mexico to Help Prevent Screwworm Spread,"

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Chris Clayton can be reached at Chris.Clayton@dtn.com

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