Genomic study targets screwworm control

Study helped identify ways to slash fly populations by targeting particular genes that control growth and development.

The University of Cincinnati is decoding the genetics of agricultural pests in projects that could help boost crop and livestock production to feed millions more people around the world, according to an announcement.

Joshua Benoit, an associate professor in the University of Cincinnati College of Arts & Sciences, contributed to genetic studies of New World screwworms that feed on livestock and thrips -- tiny insects that can transmit viruses to tomatoes and other plants.

The New World screwworm's Latin name means "man-eater," and these flies lay up to 400 eggs in open cuts or sores of cattle, goats, deer and other mammals. Emerging larvae begin gnawing away on their hosts, feeding on living and dead tissue and creating ghastly wounds, the university said.

"Sometimes, you'll see a deer missing a chunk of its head. The flies can cause small wounds to become massive injuries," he said.

Benoit and his co-authors sequenced the genome of screwworms and identified ways of slashing populations by targeting particular genes that determine sex and control growth and development or even particular behaviors that help the flies find a suitable animal host.

The study, led by entomologist Maxwell Scott at North Carolina State University, was published in the journal Communications Biology.

"Our main goal was to use the genomic information to build strains that produce only males for an enhanced sterile-insect program," Scott said.

The New World screwworm is an agricultural menace that causes billions of dollars in livestock losses each year in South America, where it is common. The fly was a scourge in North America as well but was eradicated from the U.S. in 1982 after intense and ongoing population control.

Today, a lab operated by Panama and the U.S. Department of Agriculture has established a biological barrier outside Panama City, a geographic chokepoint between the two continents.

"They rear flies in a lab, sterilize them with chemicals or radiation and dump these sterile male flies into the environment from a plane so they mate with the females and produce no offspring," Benoit said.

Year by year, agricultural experts gradually pushed the screwworm out of Texas, Mexico and most of Central America.

"They just used straight brute force and good science," Benoit said. "They just drove them down all the way to Panama."

Today, Panama and the U.S. continue to air-drop sterile screwworms over the chokepoint by the millions each week to prevent the species from moving north.

A 2016 outbreak in the Florida Keys threatened to wipe out endangered Key deer before USDA intervened, treating infected animals with a parasite medicine and releasing millions of sterile screwworms on the island chain until they disappeared.

"The U.S. still helps pay for control programs in Panama mainly because we don't want screwworms coming back here. It's the cheapest way to prevent potentially billions of dollars in damage," Benoit said.

One possible way to cut costs would be to raise only male screwworms that are intended for release so the lab wouldn't incur the huge costs of feeding female screwworms. The University of Cincinnati genetic study could help scientists cull females before they hatch. "So, you're left with surviving males. Then, you sterilize the males, and that would save a lot of money because you'd only have to raise the males for release," he said.

Next, Scott said he wants to understand how the livestock-devouring screwworm Cochliomyia hominivorax evolved as a parasitic meat eater even though similar species prefer carrion.

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