June 27, 2022 – The first high-quality genome of the desert locust — those voracious eaters of plague and devastating disgrace and the world’s most destructive migratory insect — has been produced by scientists at the U.S. Department of Agriculture Agricultural Research Service.
The desert locust (Schistocerca gregaria) genome is huge at just under 9 billion base pairs, nearly three times the size of the human genome.
“We were concerned that faced with this huge and highly likely complex desert locust genome, it would be an extremely long and difficult task. However, we were able to go from sample collection to a finally assembled genome in less than 5 months,” said entomologist Scott M. Geib of the ARS Tropical Crop and Commodity Protection Research Unit in Hilo, Hawaii, and one of the team leaders. “The desert locust is one of the largest insect genomes ever completed and it was all done by a single grasshopper.”
That one grasshopper was provided by chemical ecologist Baldwyn Torto of the International Center of Insect Physiology and Ecology (ICIPE) in Nairobi, Kenya. He and his team tracked down swarms of locusts and collected specimens all over Kenya until he had two parents whom he could breed to produce an offspring of known pedigree.
The size of the desert locust’s chromosomes is remarkable; compare them to those of the model fruit fly Drosophila melanogaster, the first insect genome ever assembled. Many of the desert locust’s individual chromosomes are larger than the entire fruit fly genome.
“With the desert locust, we were dealing with a much larger genome in much fewer pieces — about 8.8 Gb in just 12 chromosomes. Besides the fruit fly, it’s like an 18-wheeler next to a compact car,” Geib said. as if we had to resequence a typical insect genome many, many times. But with current advances in DNA sequencing technologies, we are now able to generate highly accurate insect genomes that would have been previously unapproachable.”
ARS has made the genome available to the international research community through the National Center for Biotechnology Information.
Desert locust plagues are cyclical and have been recorded since the time of the pharaohs in ancient Egypt, as far back as 3200 BC. In recent decades, desert locust swarms have occurred in 1967-1969, 1986-1989 and most recently in 2020-2022. They are wreaking havoc in East Africa, the Middle East and Southwest Asia and are threatening food security in many countries.
Their damage can be enormous. A small swarm can eat as much in a day as would feed 35,000 people; a swarm of historic proportions covering the New York City area eats as much in one day as the populations of New York, Pennsylvania and New Jersey put together, according to the Food and Agriculture Organization of the United Nations.
Current control of desert locusts largely depends on locating swarms and spraying with broad-spectrum pesticides. Ultimately, this genomics work could reduce reliance on such pesticides.
“Having a high-quality genome is a big step toward finding targeted controls,” Geib said. “It will also give us valuable information about desert locust relatives that are major pests in the Americas, such as the Mormon cricket, another swarming species that could affect 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 basis for basic and applied research.
USDA Foreign Agricultural Service coordinated this research opportunity and provided funding from the US Agency for International Development Africa Bureau through an inter-agency agreement.
The Agricultural Research Service is the principal in-house scientific research agency of the United States Department of Agriculture. Every day ARS focuses on solutions for agricultural problems in America. Every dollar invested in agricultural research results in $17 in economic impact.
Five facts about desert locusts
- The desert locust (Schistocerca gregaria) is a species of short-horned grasshopper that periodically changes its body shape, behavior, and reproduction rate in response to environmental conditions such as an abundance of rainfall and moisture.
- Pest is actually a technical term. Desert locust plagues are identified in a sequence of increasing severity based on size and geographic scale of swarm size: recession (rest), outbreak, revival, plague (maximum intensity and magnitude).
- Swarms can remain in the air for a long time. They regularly cross the Red Sea, about 300 km. They can also travel long distances: for example, from northwest Africa to the British Isles in 1954 and from West Africa to the Caribbean in about ten days in 1988. Swarms can travel up to 1000 km in one week, about the distance between San Francisco and Seattle.
- A swarm of one square kilometer can contain up to 80 million adult desert locusts.
- Each new generation in a swarm can be up to 20 times larger than the previous one.
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