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Scientists Map the Genome of Agricultural Monsters

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The University of Cincinnati is decoding the genetics of agricultural pests in a project that could help boost crop and livestock production to feed millions more people around the world.

Joshua Benoit, an associate professor in UC’s College of Arts and 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.

It’s the latest international collaboration for Benoit, who previously unraveled the genomes of dreaded creatures such as bedbugs.

Just in time for Halloween, Benoit’s new study subject is no less creepy. The New World screwworm’s Latin name means “man-eater.” These shiny blue flies with pumpkin-orange eyes 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.

A map of North America shows the gradual eradication of screwworms south into Central America.

The U.S. Department of Agriculture methodically drove screwworms out of the continental United States over the span of several decades and maintains a biological barrier in Panama. Map/USDA

“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's work demonstrates UC's commitment to research as described in its strategic direction called Next Lives Here.

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 United States in 1982 with intense and ongoing population controls.

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

“They rear flies in a lab, sterilize the larvae using chemicals or radiation and dump the sterile males into the environment by plane so they mate with the females and produce no offspring,” Benoit said.

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

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

Today, Panama and the United States continue to air-drop sterile screwworms by the millions each week over the choke point to prevent the species from moving north.

A 2016 outbreak in the Florida Keys threatened to wipe out endangered Key deer before the USDA intervened, treating infected animals for parasites 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. UC’s 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 while similar species prefer carrion.

Transmitting viruses

Benoit also contributed to a genomic study in the journal BMC Biology for an insect not much bigger than the dot over the letter i. Thrips, a tiny winged insect, are legion around the world and feed on a wide variety of crops, including soybeans, tomatoes — even cannabis. They can destroy crops both by eating them and transmitting harmful viruses.

In a study led by entomologist Dorith Rotenberg at North Carolina State University, researchers mapped 16,859 genes that helped understand the thrips’ sensory and immune systems and the salivary glands that transmit the viruses.

“The genome provides the essential tools and knowledge for developing genetic pest management strategies for suppressing thrips pest populations,” Rotenberg said.

One thrips virus is a particular agricultural concern: the spotted wilt virus, which studies have found can reduce a crop’s yield by as much as 96%.

“We’re talking hundreds of millions of dollars in losses,” Benoit said.

The study found that thrips can be finicky eaters that have unique genetic adaptations that allow them to feed on many plants. They pierce the plant and suck its juices.

Thrips have surprisingly sophisticated immune systems, the study found. Researchers identified 96 immune genes, more than many other insects studied to date.

“We mapped the genome, but we also characterized immune aspects and how they feed,” Benoit said. “It was the first study of its kind to explain what underlies their reproductive mechanisms. It was far more detailed than previous genomic studies we’ve done.”

The study was funded in part by the National Science Foundation and a UC faculty development research grant.

Benoit said the solution to a thrips infestation predictably has been pesticides. But the UC study could help find better environmental solutions, he said.

“Pesticides do not discriminate at all. The same pesticide that kills a termite can kill a bee. When you spray, it can kill other beneficial insects,” Benoit said. “So we don’t want to eradicate species as much as find better ways to control them so we don’t have to use as much pesticide.”

Reference: Scott MJ, Benoit JB, Davis RJ, et al. Genomic analyses of a livestock pest, the New World screwworm, find potential targets for genetic control programs. Commun Biol. 2020;3(424). doi:10.1038/s42003-020-01152-4

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