The first high-quality genome of the desert locust, the world’s most destructive migratory insect and a voracious feeder of plague and devastation, has been produced. The desert locust (Schistocerca gregaria) genome is nearly three times the size of the human genome, at just under 9 billion base pairs. Compare the size of the desert locust’s chromosomes to those of the model fruit fly Drosophila melanogaster, the first insect genome ever assembled. Many of the individual chromosomes of the desert locust are larger than the entire fruit fly genome. It’s the equivalent of an 18-wheeler next to a compact car.
The desert locust (Schistocerca gregaria) genome is nearly three times the size of the human genome, at just under 9 billion base pairs.
“We were concerned that, faced with this massive and very likely complex desert locust genome, it would be an extremely time-consuming and difficult task. We were able, however, to go from sample collection to a final assembled genome in less than 5 months” One of the team leaders was entomologist Scott M. Geib of the ARS Tropical Crop and Commodity Protection Research Unit in Hilo, Hawaii. “The desert locust genome is one of the largest insect genomes ever completed, and it was done entirely from a single locust.”
With the desert locust, we were dealing with a much larger genome in many fewer pieces — about 8.8 Gb in just 12 chromosomes. Next to the fruit fly, it’s like an 18-wheeler next to a compact car. It was like sequencing a typical insect genome many, many times over.
Scott M. Geib
Baldwyn Torto, a chemical ecologist at the International Centre of Insect Physiology and Ecology (ICIPE) in Nairobi, Kenya, provided that one locust. He and his team tracked down locust swarms, collecting specimens across Kenya until he had two parents with which he could breed to produce offspring with known pedigree.
Compare the size of the desert locust’s chromosomes to those of the model fruit fly Drosophila melanogaster, the first insect genome ever assembled. Many of the individual chromosomes of the desert locust are larger than the entire fruit fly genome.
“With the desert locust, we were dealing with a much larger genome in many fewer pieces — about 8.8 Gb 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.”
Through the National Center for Biotechnology Information, ARS has made the genome available to the international research community. Desert locust plagues are cyclical and have been documented since the Pharaohs of ancient Egypt, dating back to 3200 B.C. Desert locust swarms have occurred in recent decades in 1967-1969, 1986-1989, and, most recently, 2020-2022. They wreak havoc in East Africa, the Middle East, and Southwest Asia, putting many countries’ food security at risk.
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.
The majority of current desert locust control relies on locating swarms and spraying them with broad-spectrum pesticides. Ultimately, this genomics research could reduce reliance on pesticides.
“Having a high-quality genome is an important step toward finding targeted controls,” Geib explained. “It will also provide us with valuable information about relatives of the desert locust that are major pests in the Americas, such as the Mormon cricket, another swarming species that could have an impact on US food security.”
This work is part of the Ag100Pest Initiative, an ARS program to develop high-quality genomes for the top 100 arthropod pests in agriculture as a foundation for basic and applied research. USDA Foreign Agricultural Service coordinated this research opportunity and provided funding from the U.S. Agency for International Development Africa Bureau through an interagency agreement.
Five Desert Locust Facts
- The Desert Locust (Schistocerca gregaria) is a short-horned grasshopper that changes its body shape, behavior, and reproduction rate in response to environmental conditions such as high rainfall and moisture.
- The term “plague” is a technical term. Desert locust infestations are classified into four types based on the magnitude and geographical scale of the swarm: recession (calm), outbreak, upsurge, and plague (maximum intensity and scope).
- Swarms can linger in the air for extended periods of time. They travel about 300 kilometers across the Red Sea on a regular basis. They can also travel long distances, such as Northwest Africa to the British Isles in 1954 and West Africa to the Caribbean in approximately ten days in 1988. Swarms can cover 1,000 km in a week, which is roughly the distance between San Francisco and Seattle.
- A swarm of one square kilometer can contain up to 80 million adult desert locusts.
- A swarm’s new generation can be up to 20 times larger than the previous one.
