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It's a nasty, hungry pest and scientists just mapped its genome

U.S. Department of Agriculture Agricultural Research Service scientists have produced the first high-quality, highly detailed genome of the desert locust (Schistocerca gregaria), shown in its yellow-and-black form, left, that is a response to high population density and the green solitary phase.

U.S. Department of Agriculture Agricultural Research Service scientists have produced the first high-quality, highly detailed genome of the desert locust (Schistocerca gregaria), shown in its yellow-and-black form, left, that is a response to high population density and the green solitary phase. (Brandon Woo, USDA-ARS)



Estimated read time: 4-5 minutes

SALT LAKE CITY — Back in 3200 B.C., their devastation in the time of the pharaohs in ancient Egypt was a reckoning.

The dreaded desert locust is the most destructive migratory insect in the world, and scientists have uncovered additional genetic information to better understand its bipolar personality in which it goes from being a fairly benign green creature into something quite dreadful.

"What makes this nice solitary locust transform into this horrible eating machine?" pondered Kim Kaplan, a spokesperson for the U.S. Department of Agriculture.

The mapping of a genome: Scientists for the Department of Agriculture Agricultural Research Service mapped the genome of the desert locust (Schistocerca gregaria) and found it to be enormous — at just under 9 billion base pairs — nearly three times the size of the human genome.

Entomologist Scott M. Geib, with the agency's Tropical Crop and Commodity Protection Research Unit in Hilo, Hawaii, and one of the team leaders puts it this way: "The desert locust is one of the largest insect genomes ever completed and it was all done from a single locust."

That one locust was provided by chemical ecologist Baldwyn Torto with the International Centre of Insect Physiology and Ecology in Nairobi, Kenya. He and his team tracked down swarms of locusts, collecting specimens across Kenya until he had two parents that he was able to breed to produce an offspring of known pedigree.

Locust swarms of a "titanic" nature have caused all sorts of devastation to food security in places like Africa, according to media reports such as NPR, which reported on one as recently as 2020.

Thank goodness not Utah: Kaplan said that given that there can be as many as 15 grasshoppers per square yard of land that are close relatives of the desert locust in Idaho, Montana, Wyoming, Oregon, Arizona, Colorado and Nebraska, this story might have some interest. While not in Utah, the locusts are, however, related to the Mormon cricket — an insect that has its own history here.

Brigham Young once famously opined that if you kill one of those Mormon crickets, two will show up to bury their fallen comrade.

In the "Comprehensive History of The Church of Jesus Christ of Latter-day Saints," this was noted: "They came swarming from the foothills literally by millions, and descended upon the new made fields of grain. They devoured all before them as they came to it. Their appetites never abated. They were cutting and grinding all day and night, leaving the fields bare and brown behind them."

Kaplan said the genome mapping is a tremendous breakthrough in better understanding how this solitary locust turns into what they call the "gregarious" form of the same insect.

"When the right environmental conditions exist, they suddenly turn on this switch and they start turning into this voracious eater. Isn't that wild?" Kaplan said.

Just how big is this genome? "With the desert locust, we were dealing with a much larger genome in many fewer pieces — about 8.8 (gigabytes) in just 12 chromosomes. Next to the fruit fly, it's like an 18-wheeler next to a compact car," Geib said. "It was like sequencing a typical insect genome many, many times over. But with today's advances in DNA sequencing technologies, we are now able to generate extremely accurate genomes of insects that previously would have been unapproachable."

Desert locust plagues are cyclic and have been recorded since the times of the pharaohs in ancient Egypt, as far back as 3200 B.C. In recent decades, there have been desert locust swarms in 1967-1969, 1986-1989 and, most recently, 2020-2022. They cause devastation in East Africa, the Middle East and Southwest Asia, threatening food security in many countries.

Their damage can be massive. A small swarm can eat as much food in a day as would feed 35,000 people; a swarm of historic proportions covering the area of New York City eats in one day the same amount as the population of New York, Pennsylvania and New Jersey combined, according to the Food and Agriculture Organization of the United Nations.

Drought as a concern: Mormon crickets can show up in times of drought, which Utah is experiencing in an extreme way.

Bret Selman, a rancher in Box Elder County, spotted Mormon crickets this spring and was part of a multifamily effort to stomp them out.

"A bunch of us got together and sprayed them. We are not seeing them now. I don't know if the spring storms killed them or our spray effort," he said.

They treated about 30,000 acres. Between the pesticide treatment and the work of the seagulls (they ate quite a few) the pests were eradicated.

Mormon cricket outbreaks have also been reported in Sanpete and Duchesne counties.

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Amy Joi O'Donoghue

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