The opening of the sterile fly dispersal facility in Edinburg, Texas, in mid-February marked a major step forward in the control of New World Screwworm, Cochliomyia hominivorax, said Dr. Rosslyn Biggs, DVM and Oklahoma State University Extension beef cattle specialist, in a letter called Cow-Calf Corner.
The facility is intended to allow the USDA to distribute millions of sterile male flies, strengthening the biological barrier designed to prevent establishment of the pest, Biggs said.
The USDA also announced plans for a domestic sterile fly production facility nearby, she said. The production plant represents an investment of roughly $750 million and is expected to produce up to 300 million sterile flies a week when up to speed, reducing reliance on international production and significantly expanding preparedness and response capacity.
A LOOK BACK
New World Screwworm was eradicated from the continental US decades ago through a coordinated effort that pushed the pest into Central America, and for years a biological barrier was maintained in Panama, Biggs said. But the fly resurfaced in southern Mexico in late 2024.
While the US remains free of an established NWS population, recent developments, including sterile fly release in Texas, expanded treatment options, and new infrastructure investments, highlight continued concern among animal health officials, she said.
NWS larvae infest open wounds and feed on living tissue, causing pain, swelling, foul odor and rapid tissue damage that can be fatal in less than two weeks if untreated, Biggs said. Female flies lay eggs in wounds, mucous membranes and body openings.
In cattle, risk is highest after branding, tagging, dehorning, castration and at newborn navels, though even minor injuries can be targeted, she said. Because females mate only once, control has relied on releasing sterile males to disrupt reproduction.
STERILE FLY SUCCESS
The sterile insect technique historically has been the hallmark of screwworm control and eradication, Biggs said. Sterile fly release has expanded into areas of northern Mexico and strategic locations up to 50 miles north into Texas.
The goal is to create a preventive buffer zone inside the US, not just in Mexico, to intercept any flies that might move north, she said. Movement controls also have been part of the response, and southern border ports between the US and Mexico remain closed to live ruminants.
Treatment options for control and prevention also have expanded, including emergency approval for macrocyclic lactone products including Ivomec (ivermectin) and Dectomax (doramectin), Biggs said. ExZolt Cattle-CA1 (fluralaner) also has been approved conditionally as a topical solution for prevention and treatment.
Use of these products in response protocols may occur under veterinary guidance and, in some cases, extra-label drug use provisions, she said.
CATTLE, BEEF RECAP
The USDA reported formula and contract base prices for live FOB steers and heifers this week ranged from $247.79 per cwt to $251.69, compared with last week’s range of $242.46 to $255.40 per cwt. FOB dressed steers and heifers went for $387.65 per cwt to $391.91, compared with $381.78 to $394.78.
The USDA choice cutout Friday was up $1.95 per cwt at $379.84 while select was up $3.52 at $374.31. The choice/select spread narrowed to $5.53 from $7.10 with 58 loads of fabricated product and 15 loads of trimmings and grinds sold into the spot market.
The USDA-listed the weighted average wholesale price for fresh 90% lean beef as $433.00 per cwt, and 50% beef was $159.03.
The USDA said basis bids for corn from feeders in the Southern Plains were unchanged at $0.98 to $1.12 a bushel over the Mar corn contract, which settled at $4.38 3/4, up $0.05 1/2.
No live cattle delivery intentions were posted Friday.
The CME Feeder Cattle Index for the seven days ended Thursday was $372.79 per cwt, down $0.38. This compares with Friday’s Mar contract settlement of $355.42, down $6.22.