US and Mexico Release Millions of Sterile Flies as Cattle Border Prepares to Reopen Following New World Screwworm Outbreak

The United States and Mexico have intensified coordinated sterile insect releases to suppress New World screwworm as the US-Mexico cattle border moves toward a phased reopening on 24 August, while Texas confirms 41 of 42 total US cases — triggering large-scale containment operations and raising urgent concerns for livestock, wildlife and rural economies on both sides of the border.

The United States will begin a phased reopening of its southern border to Mexican cattle imports on 24 August 2026, starting with the Douglas-Agua Prieta crossing from Sonora into Arizona — ending a closure of more than a year triggered by the New World screwworm outbreak in Mexico, which has now spread to 29 of Mexico’s 32 states with approximately 1,792 active cases.

The United States and Mexico jointly retrofitted a facility in southern Mexico that began producing sterile New World screwworm flies this summer, becoming one of two facilities currently producing sterile flies for dispersal throughout the region. The facility is expected to produce up to 100 million sterile flies per week once fully operational, distributed by air across the worst-affected areas.

A new $750 million screwworm-fighting facility in South Texas is now ahead of schedule, with Agriculture Secretary Brooke Rollins confirming construction has moved to 24-hours-a-day, seven-days-a-week operations to bring it online by next spring — significantly ahead of the original November 2027 target.

The USDA confirmed that the reopening will be subject to a joint action plan, with all imported Mexican cattle undergoing inspection in the US to prevent entry of screwworm larvae. The northern Mexican states of Sonora and Chihuahua remain the lowest-risk Mexican states due to their established animal health inspection programmes and distance from southern Mexico where most cases have been detected.

Despite the border reopening, containment efforts remain critical. The US has confirmed 42 cases since June 3, with 41 in Texas and one in New Mexico. Texas Agriculture Commissioner Sid Miller welcomed the reopening while urging continued vigilance, noting the significant impact the closure has had on producers and the wider cattle industry.