Mexico and US Double Down on Sterile Flies to Beat Screw-Worm and Reopen the Border

The sterile fly production plant in Chiapas is designed to produce millions of male screws per week, enough to suppress the pest across the affected regions through sustained aerial release. It is not yet at full capacity. A new US-developed technology that produces only male sterile flies, which would eliminate the need to sort flies by sex before release and potentially double the plant's effective output, is under review by Cofepris, Mexico's health regulator. The review could take 12 to 18 months, if historical timelines hold.

President Claudia Sheinbaum announced Monday that Mexico and the United States are intensifying their joint screw-worm eradication campaign, building on the biological control model that eliminated the pest from North America in the 1970s and 1980s. The stakes are straightforward: the border for Mexican cattle exports has been closed since December 2025, when the USDA detected screw-worm larvae in cattle at border inspection points. The industry generated roughly $3.5 billion in export revenue in 2024. That revenue has dropped to near zero.

The strategy depends on the sterile insect technique, which uses radiation-sterilized male flies that are released by aircraft to mate with wild females and produce no offspring. The same technique worked before, the original US-Mexico campaign, which cost roughly $750 million in today's dollars, pushed the pest south of the Isthmus of Panama and kept it out of North America for nearly 40 years. The current outbreak, first detected in late 2025, proves that eradication is not a one-time achievement. It requires ongoing investment.

"The experience from decades ago shows that this method works," Sheinbaum said. "We are reinforcing it with new technology and binational cooperation."

The quote is accurate, but it glosses over the gap between the method and the results. The Chiapas plant needs to reach full production. The new male-only fly technology needs regulatory approval. The aerial release program needs to cover all affected states, including Chiapas, Tabasco, Campeche, Veracruz, and the Yucatan Peninsula. The USDA has not given a timeline for reopening the border, and the agency's position is that it will wait until it sees measurable progress.

Some experts have raised doubts about whether the eradication can succeed a second time. Screwworm populations in Central America have grown more resilient since the original campaign. Livestock movements across informal border crossings in southern states complicate containment. The 1970s campaign had the advantage of a largely isolated pest population. The current outbreak is more widespread before containment even began.

The economic damage extends beyond the cattle producers. The agricultural supply chain, feed suppliers, veterinary distributors, trucking companies, depends on the cattle trade. The agricultural sector accounts for roughly 4 percent of Mexico's GDP. A prolonged border closure has ripple effects through rural economies in Sonora, Chihuahua, and the southern states.

The campaign moves forward. The sterile flies are being bred. The release planes are being prepared. The cattle wait in their pens. The border stays closed. The question is whether the Chiapas plant can reach full capacity before the industry collapses further.

The Sheinbaum administration's approach to the screw-worm crisis reflects a broader pattern in Mexican agricultural policy: reliance on biological control methods that require sustained investment and cooperation with US agencies. The approach has worked before. But the current outbreak is testing whether the institutional memory and budget commitment still exist to replicate the success of the 1970s. The Chiapas plant is the test. If it reaches full production on schedule, the border could reopen within 18 months. If it does not, the cattle industry faces a longer wait that will bankrupt some of the smaller producers who cannot survive another year without export revenue.\n\nSource: Tabasco Hoy

The broader context for the screw-worm crisis is the state of Mexico's livestock health infrastructure. The country has roughly 35 million head of cattle spread across 31 states, according to the Agriculture Secretariat's 2025 livestock census. The inspection infrastructure at the US border includes 12 official entry points for live cattle, each equipped with veterinary inspection stations. The screw-worm larvae were detected at one of those stations in December 2025, triggering the closure of all 12. The USDA has not said whether the outbreak originated in Mexico or arrived through the movement of animals from Central America, where screwworm has remained endemic since the original eradication campaign.

The question matters for the eradication strategy. If the outbreak originated from a smuggled animal passing through the southern border with Guatemala, the containment effort requires cooperation across three countries. If it was a domestic Mexican outbreak from a population that survived the original campaign in a remote area, the strategy is different. The Sheinbaum administration has not publicly addressed the question of origin, and the USDA has not released its epidemiological analysis. The answer would tell ranchers how long they will be waiting.