Sequencing the genome of a voracious desert locust

The first high-quality genome of the Desert Locust – those voracious eaters of plague and infamy of devastation and the world’s most destructive migratory insect – has been produced by scientists at the United States Department of Agriculture’s Agricultural Research Service .

The locust genome (Schistocerca gregaria) 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 most likely complex locust genome, it would be extremely time-consuming and difficult work. However, we were able to go from collecting samples to a final assembled genome in less than 5 months, said entomologist Scott M. Geib of the ARS Crop Protection and Tropical Products 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 made from a single locust.”

This locust 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, collecting specimens across Kenya until he had two parents he was able to raise to produce offspring of known pedigree.

The size of the locust chromosomes is remarkable; compare them to those of the model fruit fly Drosophila melanogaster, the first insect genome ever assembled. Many individual locust chromosomes are larger than the entire fruit fly genome.

“With the desert locust, we were dealing with a much larger genome in far fewer pieces – around 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. But with current advances in DNA sequencing technologies, we are now able to generate highly accurate insect genomes that would have been inaccessible before. .”

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 early as 3200 BC. They wreak havoc in East Africa, the Middle East and Southwest Asia, threatening food security in many countries.

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

Current Desert Locust control depends primarily on locating swarms and spraying them with broad-spectrum pesticides. Ultimately, this genomic work could reduce dependence on these pesticides.

“Having a high-quality genome is a big step toward finding targeted controls,” Geib said. “It will also give us valuable information about relatives of the desert locust that are major pests in the Americas, such as the Mormon cricket, another swarming species that can impact US food security.”

This work is part of the Ag100Pest initiative, an ARS program aimed at developing high-quality genomes for the top 100 arthropod pests in agriculture as a basis for basic and applied research.

The USDA Foreign Agricultural Service coordinated this research opportunity and provided funding from the Africa Bureau of the United States Agency for International Development under an interagency agreement.

Five facts about the Desert Locust

  • The Desert Locust (Schistocerca gregaria) is a species of short-horned grasshopper that periodically changes its body shape, behavior, and reproductive rate in response to environmental conditions such as abundant rainfall and humidity.
  • Plague is actually a technical term. Desert Locust infestations are identified in a sequence of increasing severity depending on the magnitude and geographical scale of the swarm size: recession (calm), upsurge, upsurge, invasion (maximum intensity and extent).
  • Swarms can stay in the air for long periods. They regularly cross the Red Sea, over about 300 km. They can also cover long distances: For example, from North West 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 1,000 km in a week, or about the distance between San Francisco and Seattle.
  • A swarm of one square kilometer can contain up to 80 million adult locusts.
  • Each new generation in a swarm can be up to 20 times larger than the previous one.

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