Editor's Note: Each year, DTN publishes our choices for the Top 10 ag new stories of the year -- issues and events -- as selected by DTN analysts, editors and reporters. This year, we're counting them down from Dec. 18 to Dec. 31. On Jan. 1 and Jan. 2, we will look at some of the runners-up for this year. Today, we continue the countdown with No. 8: How New World screwworm is moving closer to the United States and what is been done to prevent it from entering the country. This has included closing the border to Mexican cattle imports and constructing sterile fly facilities to continue to combat the pest. No NWS cases have been found in the U.S. as of publication. The closest case was 70 miles from the U.S. border.

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REDFIELD, Iowa (DTN) -- The U.S. livestock industry has known for years that a foreign animal disease could be devastating to farmers and ranchers, but the industry was likely unaware of how a pest like New World screwworm (NWS) would affect the country.

In November 2024, the U.S./Mexican border was closed in hopes of preventing NWS from entering the country; however, during the year it moved north through Mexico and closer to the U.S. So far, the safety preventatives have kept the pest out of the U.S.

The U.S. imported 1.2 million head from Mexico annually in both 2023 and 2024 of feeder cattle from Mexico to be fed in feedlots and slaughtered. The news of a closed border affected cattle markets as well, moving upward with the thought of a smaller supply.

The border reopened in February, and some cattle were able to move across the border after going through stringent quarantine and treatment to prevent any of the pests from riding across the border. DTN reported in late October that the number of imported cattle into the U.S. from Mexico has fallen to 230,000 head in 2025, allowed to cross at the ports of entry and make their way to southern feedyards.

Since the biological barrier at Panama had been broken in late 2024, animal health officials in Central America, Mexico and the U.S. started working together to find the best way to fight the NWS. The best option for areas where the insect had been found is the sterile insect technique (SIT). In the 1930s, entomologists determined the NWS fly only mates once; thus, if the male flies are sterilized and released to mate with females, there would be no offspring from the mating. This would lead to the SIT being used widespread. Currently, a facility in Panama produces 100 million sterile flies per week, which isn't enough to keep up with the demand.

USDA officials announced that Moore Airbase in Texas will be the location of a sterile fly distribution facility to be ready for distribution in early 2026. Later, USDA also announced a sterile fly production facility will be built at the same location. This facility will take longer and be ready in 2027. It will produce 100 million flies per week and ramp up to 300 million flies per week when in full production. A production facility is also planned to open by mid-2026 in Metapa, Mexico. All this production will help to eradicate the NWS fly.

NWS are fly larvae that infest mammals and birds, feeding as they go like a screw being driven into wood. Symptoms in these animals include irritated behavior, head shaking, smell of decay, evidence of fly strike and presence of fly larvae in the wounds, according to the Animal and Plant Health Inspection Service (APHIS). NWS can cause serious damage and even kill an animal. It can affect humans as well, if people are traveling to infected areas and a wound is present. Overall, it's important for people to be aware of what's happening in the area they are living or traveling to.

No livestock owner in the U.S. wants to deal with NWS as it will likely affect not just animals, but also livestock markets. Looking at the big picture, it has already been affecting cattle crossing the border to be fed in U.S. feedlots. Be sure to read about how a Texas feedlot has been affected by the closure and how it has affected producers in Mexico, see: https://www.dtnpf.com/….

USDA officials have started a website for keeping the public updated on protecting the U.S. from NWS. Visit this website at: https://www.aphis.usda.gov/….

To read about the U.S. human case in August, see: https://www.dtnpf.com/….

To read about the closest NWS has come to the U.S. border, see: https://www.dtnpf.com/….

To learn more about current prevention efforts, read: https://www.dtnpf.com/….

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See Editors' Notebook, "Counting Down Top Ag Stories of 2025," https://www.dtnpf.com/…

Other countdown stories:

-- Top 10 Ag Stories of 2025: No. 10, "From RFS Exemptions to E15 in CA, Biofuels Policy Makes News in 2025," https://www.dtnpf.com/…

-- Top 10 Ag Stories of 2025: No. 9, "Glyphosate Faces Uncertain Future as Lawsuits Mount and Science is Questioned," 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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