2026-11-09 from ctvnews.ca

MEXICO CITY/WASHINGTON -- For decades, planes dropped billions of factory-bred sterile flies to keep the flesh-eating New World screwworm out of North America’s cattle. That controls the pest because sterile males mate with wild females – whose eggs then fail to hatch.

But the strategy works only if the supply of flies never runs short.

When the parasite broke through a barrier of sterile flies in Panama in early 2023, the region lacked the capacity to contain it. Efforts to scale up the fly population still lag more than three years into the outbreak, after the parasite ripped through Mexico and into the United States, according to Reuters interviews with 15 current and former officials and experts in the US, Mexico and Panama.

Short on flies, the administration of U.S. President Donald Trump closed the border with Mexico to cattle imports for more than 15 months starting in May 2025, disrupting a multibillion-dollar trade. As the border began to reopen this year, dozens of cases were confirmed in US cattle.

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