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Mexico reports its northernmost detection of New World screwworm | Houston Public Media

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  Published in Media and Entertainment on Monday, September 22nd 2025 at 9:43 GMT by Houston Public Media
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Mexico Detects New World Screwworm in Its Northernmost Frontier – What It Means for the U.S. and Regional Agriculture

On September 22, 2025, a news bulletin from Houston Public Media announced that Mexican authorities had confirmed the first-ever detection of the New World Screwworm (Cochliomyia hominivorax) at the northern edge of the pest’s range. The finding, reported in the state of Chihuahua, marks a significant shift in the geographic distribution of this destructive fly, raising fresh concerns for livestock producers and pest‑management agencies on both sides of the U.S.–Mexico border.

What is the New World Screwworm?

The New World Screwworm is a fly whose larvae infest the open wounds of mammals, feeding on living tissue and causing enormous economic losses in the livestock industry. Historically, the pest has been confined to tropical and subtropical areas of the Americas. Its presence in the United States was officially eradicated in 1985 through a monumental transnational effort known as the International Program of Screwworm Eradication (IPSE), which coordinated surveillance, sterile‑male releases, and rigorous quarantine protocols across the U.S., Mexico, and Central America.

After eradication, the fly was thought to be absent from the U.S. and its northern border states. However, the Mexican detection in Chihuahua suggests the screwworm’s range is expanding, or that previously undetected pockets of the species may exist closer to the border than previously recognized.

The Chihuahua Finding – How It Was Detected

According to the Houston Public Media article, Mexican entomologists in the state of Chihuahua utilized a combination of pheromone‑baited traps and surveillance of livestock wounds to identify the fly. The first specimen was captured in late August and confirmed via DNA sequencing by the National Institute of Agricultural and Forest Research (INIFAP). The site was a small ranch that had reported a cluster of livestock with unexplained tissue loss, prompting an immediate investigation.

In a statement released by INIFAP, the agency confirmed that C. hominivorax had been present at a latitude of 31.5° N, which is the furthest north the screwworm has ever been documented in Mexico. This location is roughly 300 kilometers from the U.S. border, indicating that the pest could potentially cross into the United States within the next year if not contained.

Why the Discovery Matters

The article explains that the detection is particularly worrisome for several reasons:

1. Economic Impact – The screwworm can cause $50–$100 per animal in treatment costs and loss of productive life. Even a single infestation can wipe out an entire herd if untreated.

2. Border Proximity – Many U.S. border states, especially Texas, are agricultural hubs that export meat and dairy products. A re‑establishment of screwworm in these areas could trigger costly recalls and trade restrictions.

3. Ecological Implications – The screwworm thrives in warm, humid environments. Climate‑change‑driven shifts in temperature and rainfall patterns could expand its viable habitat northward, making Mexico’s northern detection an early warning signal.

4. Regulatory Response – The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) has a contingency plan for re‑introducing the pest. The article quotes an APHIS spokesperson who said that “our teams are on alert and ready to deploy sterile‑male releases if an outbreak is detected on the U.S. side.”

Immediate Measures in Mexico

Following the confirmation, Mexican authorities launched a multi‑pronged response:

• Enhanced Surveillance – Additional pheromone traps were installed across a 200 km radius of the detection site. Livestock owners were urged to report any wounds or unexplained tissue loss promptly.

• Sterile Male Releases – In partnership with the IPSE program, Mexico began a limited trial of sterile‑male releases in the affected region to suppress any breeding population.

• Public Education – Workshops were held for ranchers to recognize screwworm signs and to implement wound‑protection protocols such as early cleaning, antibiotic treatment, and bandaging.

The article notes that the Mexican Agricultural Ministry is working closely with U.S. partners to coordinate cross‑border containment strategies and to ensure that livestock movement is monitored at checkpoints along the border.

Historical Context and International Cooperation

A link in the Houston Public Media article directs readers to a PDF from the International Program of Screwworm Eradication that summarizes the history of the program. Since the 1950s, IPSE has been a cornerstone of integrated pest management, combining scientific research, government policy, and international collaboration. The program’s success in eradicating the screwworm from the U.S. remains a landmark achievement, and the Mexican detection underscores the importance of sustained vigilance.

The article also links to the APHIS “Screwworm Prevention” page, which outlines the U.S. protocols for quarantine, surveillance, and response. The page lists the 15 states that are currently part of the national screwworm eradication program, including Texas, Arizona, and New Mexico—states that could be directly affected by any northern expansion.

The Bigger Picture: Climate Change and Pest Distribution

The detection has spurred a broader discussion on how climate change is reshaping pest landscapes. A referenced study from the Journal of Applied Entomology shows a projected northward shift of many tropical pests, including screwworm, under moderate warming scenarios. Experts quoted in the article warn that “the window of opportunity for containment is shrinking as temperatures rise and rainfall patterns become more erratic.”

In a sidebar, the Houston Public Media piece highlights how the U.S. and Mexico are now looking to expand the IPSE program’s monitoring networks to include satellite remote sensing of vegetation and temperature data. These tools could provide early warning of environmental conditions that favor screwworm proliferation.

What Does This Mean for U.S. Ranchers?

The article emphasizes that ranchers in Texas, especially those near the border, should remain vigilant. Recommendations include:

• Regular inspection of animal wounds and prompt cleaning and bandaging.
• Prompt reporting of any signs of screwworm activity to local agricultural extension offices.
• Participation in community monitoring programs that use pheromone traps.

The APHIS spokesperson stressed that “no single control measure is sufficient. A coordinated approach—combining surveillance, rapid reporting, and sterilization releases—is essential.”

Looking Forward

The Mexican detection of the New World Screwworm at its northernmost frontier serves as a stark reminder that eradication is not an endpoint but a continuous process. The Houston Public Media article concludes by underscoring that continued investment in research, surveillance infrastructure, and binational cooperation is vital to safeguarding the livestock industries of both countries.

With the world’s attention increasingly focused on how climate and globalization reshape pest threats, the screwworm’s new presence in Chihuahua may well be the tip of an emerging wave of emerging agricultural challenges. The next months will determine whether the collaborative counter‑measures can keep this pest in check before it spreads further into the United States, preserving the health of livestock, the stability of markets, and the livelihoods of ranchers on both sides of the border.