USDA Rushes to Eradicate the Screwworm Fly Again

U.S.-funded researchers in Panama are preparing for the first outdoor test of genetically modified screwworm flies, aiming to neutralize the parasite that has spread from Central America into the United States (Reuters, subscription).

What’s going on: “The Trump administration has touted the development of the genetically modified fly, called NovoFly, as ‌a game-changer in the fight against New World screwworm. Widespread infestations could cause estimated losses of more than $1 billion to Texas’ livestock industry and spread to other U.S. states.”

• Screwworms—flesh-eating flies whose females lays eggs in the open wounds and mucous membranes of warm-blooded animals—were detected in Texas for the first time in decades.
• The flies, which were officially declared eradicated from the U.S. in 1966, eventually kill their hosts if left untreated.

Why it’s important: The longtime fix was dispersing sterile screwworm flies, now primarily produced at the Panama site—but there aren’t enough to eradicate the parasite in the large area to which it’s now spread.

• “[E]xperts say ⁠they need 500 million a week to push screwworm flies back to the geographic boundary of the Darien Gap, the stretch of rainforest between Panama and Colombia.”

How it works: NovoFly is genetically engineered to produce only males. Once these males are sterilized, they could be released to mate with females, which will lay unfertilized eggs.

• Female screwworm flies generally mate only once.

What’s next: After initial tests in Panama, larger NovoFly trials—in which researchers will release 50,000 of the insects every few days—will be conducted.

• If NovoFly does well in the trials, the U.S. Department of Agriculture could scale up production at a new sterile-fly production site in Texas that’s scheduled to open in 2027.
• Mexico could begin producing male flies by the end of 2026.

The bottom line: Though the U.S. Department of Agriculture hopes to eradicate the parasite much faster this time than it did in the 1960s, “it will likely take more than a year to control the pest.”