The resurgence of the New World screwworm (Cochliomyia hominivorax) or NWS, in North America marks a pivotal moment in the region’s ongoing struggle to safeguard livestock, wildlife, and rural economies. Once considered a triumph of entomological science and international cooperation, the eradication of this devastating parasite is now under threat, demanding a rapid, coordinated response that leverages both historical lessons and cutting-edge innovations in pest management.

I. The Current State of Affairs: Outbreak Scope and Response

As of mid-2025, the New World screwworm outbreak has escalated to a level not seen since its eradication from the United States in the late 20th century. The pest, historically endemic to parts of South America and the Caribbean, began a northward advance in 2022, breaching containment lines and spreading through Central America. Panama experienced an explosion of screwworm detections, rising from an average of 25 cases per year to more than 6,500 cases in 2023. By 2024–2025, infestations were confirmed as far north as Veracruz and Oaxaca, Mexico. While the screwworm has not yet crossed into the United States, its proximity has triggered a wave of biosecurity measures and economic concern among livestock producers and public health officials[1][2][3][4].

The United States Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS), initially resumed some livestock imports under strict quarantine and pre-export treatment protocols in January 2025. However, these protocols were suspended in May 2025 by Secretary Rollins, who halted all live animal imports through ports of entry along the southern border to prevent the pest’s entry via legal trade routes. Despite these measures, the risk remains high due to illegal crossings and the pest’s capacity for rapid dispersal. The economic stakes are enormous: Adjusting for inflation, an NWS outbreak comparable to the 1976 event could result in annual losses of $732 million for Texas producers and a total economic impact of $1.8 billion on the Texas economy [5].

M3 is in discussions with several stakeholders, including federal agencies, scientific and engineering partners, tribal governments—most notably the Colville Confederated Tribes—academic researchers at institutions such as the University of Florida and Texas A&M, as well as congressional offices and cattle and livestock associations. Their coordinated efforts are shaping both the immediate response and the longer-term strategy for containment and eradication.

II. Historical Use of SIT Against Screwworm: A Legacy of Innovation

The story of screwworm eradication in North America is inseparable from the development and deployment of the Sterile Insect Technique (SIT). SIT is a species-specific, non-chemical method that involves the mass release of sterilized male flies into the wild. Because female screwworms mate only once in their lifetime, the saturation of wild populations with sterile males leads to a dramatic reduction in viable offspring, ultimately collapsing the pest population[6].

This approach was pioneered in the United States in the 1950s and 1960s, culminating in the complete eradication of screwworm from the U.S. by 1966. The program’s success was extended southward, with Mexico declared screwworm-free by 1991. To prevent re-invasion, a bi-national buffer zone and production facility were established in Panama, which continues to serve as a critical line of defense against the pest’s northward migration[3][6].

SIT’s precision and environmental safety have made it the gold standard for screwworm control, avoiding the ecological and health risks associated with chemical insecticides. The legacy of SIT is not merely historical; it remains the foundation of current and future eradication efforts.

III. The Shift to Modular SIT: A New Rapid Response Frontier

The COPEG facility in Panama is currently producing up to 100 million sterile flies per week [7] to combat the new world screwworm outbreak, though it was originally designed for a capacity of approximately 20–25 million sterile flies weekly. Recently, the USDA allocated $21 million to support the renovation of a sterile NWS fly production facility in Metapa, Chiapas, Mexico, which will add an additional 60–100 million sterile flies per week to the overall production capacity [7]. Furthermore, the STOP Screwworms Act is seeking $300 million in funding to develop a large-scale sterile fly facility in Texas, reflecting congressional interest in expanding domestic production capabilities [8].

While these large, centralized facilities are critical for sustained, high-volume suppression campaigns, the current outbreak has highlighted the limitations of relying solely on such centers. Geographic distance from emerging outbreak zones and the lengthy timelines required for construction or retrofitting can delay the deployment of sterile insects, reducing the effectiveness of rapid response efforts. This underscores the need for a more flexible and resilient production and distribution network to ensure timely delivery of sterile insects to affected areas.

IV. Implications for Livestock Producers, Public Health, and Regional Economies

The threat of screwworm re-establishment in the United States carries profound implications for animal health, food security, and rural livelihoods. Livestock producers face the prospect of devastating losses, not only from direct infestations but also from trade disruptions and increased biosecurity costs. Public health officials must contend with the zoonotic potential of screwworm, which can infect a wide range of warm-blooded hosts, including humans. Regional economies, particularly those dependent on cattle, bison, and equine industries, are at risk of significant downturns if the pest is not contained[2][4][6].

The deployment of modular SIT units, supported by robust surveillance and rapid response protocols, offers a pathway to mitigate these risks. By enabling swift, localized intervention, this approach can prevent the establishment of new populations, protect animal welfare, and preserve the economic vitality of affected regions.

V. A New Chapter in the Battle Against Screwworm

The renewed threat of the New World screwworm in North America is a stark reminder that biosecurity is an ongoing, dynamic challenge. The integration of modular SIT units into the response arsenal, powered by public-private-partnerships and technological innovation, marks a turning point in the fight against this formidable pest. As stakeholders mobilize to confront the current outbreak, the lessons of history and the promise of new tools offer hope that the hard-won gains of the past can be preserved—and that the frontlines of biosecurity can be held, even in the face of evolving threats.

Works Cited

1. AgriLife Today. Texas A&M AgriLife announces New World screwworm fact sheet. 2025 May 20. Available from: https://agrilifetoday.tamu.edu/2025/05/20/texas-am-agrilife-announces-new-world-screwworm-fact-sheet/

2. American Farm Bureau Federation. New World Screwworm Moves Beyond Containment Threshold. 2025 May 22. Available from: https://www.fb.org/market-intel/new-world-screwworm-moves-beyond-containment-threshold

3. USDA APHIS. New World screwworm and equines updates (as of January 17, 2025). 2025 Jan 17. Available from: https://www.aphis.usda.gov/news/program-update/new-world-screwworm-equines-updates-january-17-2025

4. CIDRAP. USDA suspends southern border livestock imports over New World … 2025 May 12. Available from: https://www.cidrap.umn.edu/misc-emerging-topics/usda-suspends-southern-border-livestock-imports-over-new-world-screwworm

5.USDA APHIS. Historical Economic Impact Estimates of New World Screwworm in the United States. 2025 Jan. Available from: https://www.aphis.usda.gov/sites/default/files/nws-historical-economic-impact.pdf

6. Sentient Media. Screwworm Outbreak Prompts U.S. to Halt Livestock Imports from … 2025 May 20. Available from: https://sentientmedia.org/screwworm-outbreak-halt-livestock-imports-from-mexico/

7. USDA. Update on USDA Efforts to Fight New World Screwworm in Mexico. 2025 May 27. Available from: https://www.usda.gov/about-usda/news/press-releases/2025/05/27/update-usda-efforts-fight-new-world-screwworm-mexico

8. Texas Farm Bureau. TFB urges support for domestic sterile fly facility. 2025 May 15. Available from: https://texasfarmbureau.org/tfb-urges-support-for-domestic-sterile-fly-facility/