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A newly detached umbilical cord is a favorite target for the screwworm fly, so treating the umbilicus as well as after dehorning helps prevent infestations.
Just as with the Asian longhorned tick, however, the best tools at your disposal are your eyes, according to Bud Dinges, DVM, Texas state veterinarian and executive director of the Texas Animal Health Commission( TAHC).
The first NWS larvae infestation was discovered in South Texas in June and the pest has since spread to 16 counties in South Texas. TAHC, USDA veterinarians and others reacted quickly, initiating sterile fly dispersion while setting up infested zones around each case and surveillance zones around the infected zone. While cattle movement is not stopped, each zone has specific requirements before cattle can move around or out of the zones.
The good news is the NWS fly will eventually be pushed out of the U. S. because it’ s been done before. The bad news is it could take a decade or more to accomplish.
“ Keep in mind that we officially eradicated them from the United States in 1966 and it was the early‘ 80s before we stopped seeing cases in the United States,” Dr. Dinges told the Cattle Health and Well-Being Committee of the Academy of Veterinary Consultants.“ And then it was 1991 before New World Screwworms were pushed back out of Mexico into Central America.”
Back then, there were no movement controls and screwworm infestations spread widely, with as many as 91,000 cases in Texas alone by 1972, Dr. Dinges said. Now, with strict regulations on cattle movement in infected and surveillance zones, spreading invasive NWS with wheels is less likely to occur.
The sterile fly technique is still the ultimate method and eradication tool. The problem is, while production capacity to produce the irradiated sterile flies is ramping up, it’ s not at the capacity needed to wage an all-out effort to push the NWS out of the U. S. into Mexico, then out of Mexico to Central America where they are endemic.
A facility in Panama can produce 100 million sterile pupae, which are spread by airplane and ground stations to molt into sterile screwworm flies. A facility in Mexico recently came online, increasing the number of sterile pupae available to disperse each week. Hopefully, it will ramp up to 100 million per week by year’ s end.
A new facility is being built in South Texas to increase sterile pupae production by April 2027. It will initially produce 100 million sterile pupae a week with a goal of 300 million by the end of 2028.
Given the current production of sterile pupae, distribution is occurring in the affected South Texas counties and along a portion of the Rio Grande River which forms the border between Texas and Mexico.
In addition to ramped-up sterile pupae production, a new technology, NovoFly TM, produces only male sterile screwworm flies. That is important because it is the male sterile flies that reduce NWS by mating with wild females, which only mate once. This produces sterile eggs which when laid in wounds, don’ t hatch into larvae. The current sterilization process produces both male and female sterile flies. Implementing NovoFly TM will essentially double the number of sterile male flies available.
The technology now awaits EPA approval. When approved, it can be implemented in the present sterile fly production facilities.
Diligence by South Texas beef producers, veterinarians and everybody else is essential in detecting and reporting any new infestations. But South Texas ranchers are up to the challenge, according to Stephen Diebel, a rancher from Victoria, Texas, and president of the Texas & Southwestern Cattle Raisers Association.
The reason? Texas had a plan and the plan worked, he said.
“ When we formed the Screwworm Coalition in early spring of 2025, it was very apparent that we needed a plan in place( to
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