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Agence France-Presse

The coronavirus isn’t the only plague making headlines this year – locusts are devastating crops in several parts of the world, and now scientists are discovering why the pest forms destructive swarms.
On its own, a locust is fairly harmless. But so-called solitary locusts can undergo a metamorphosis, changing colour and joining together with millions of others in catastrophic clouds that strip fields.
So what prompts locusts to transform from solitary to “gregarious”?
A study published Wednesday in the journal Nature reveals the secret lies in a pheromone.
Almost like an irresistible perfume, the chemical compound is emitted by locusts when they find themselves in proximity to just a few others of their kind.
Battered by coronavirus and swine fever, is China ready for locusts?
The chemical attracts other locusts, who join the group and also begin emitting the scent, creating a feedback loop that results in enormous swarms.
The discovery offers several tantalising possibilities, including genetically engineering locusts without the receptors that detect the swarming pheromone, or weaponising the pheromone to attract and trap the insects.
The study comes as record numbers of locusts devour crops in east Africa and threaten the food supply in Pakistan.


It focused on the migratory locust, the most widely distributed species of the insect, and examined several compounds produced by the bug.
It found that one in particular – 4-vinylanisole, or 4VA – appeared to attract locusts when emitted, and that the more locusts flocked together, the more 4VA they emitted.
The team, led by Le Kang, a professor at the Chinese Academy of Sciences, found solitary locusts began releasing 4VA when just four were placed together in a cage.
The team then examined how the locusts picked up the scent, and isolated the part of the locust antennae responsible for detecting the swarming pheromone.
China’s green zombie fungus could hold key to fighting East Africa’s locusts
And from there, they found the gene necessary for the detection process and produced genetically modified locusts lacking the key Or35 gene.
The “mutant locusts lost their attraction to 4VA compared with the wild-type locusts”, the study said.
The discoveries open up several possibilities for tackling the voracious pests, including using genetic modification, or tracking 4VA production to predict where swarms may be forming.

There are other avenues too, including weaponising the chemical, by using a synthetic form of it to bait traps to catch locusts.
Kang and his team tried this, setting up traps in both controlled settings and in the field, and in both cases found the locusts were effectively lured.
“Optimisation and adjustment are necessarily required from the experiments to practical application,” Kang said.
But he said the traps were “significantly efficient” and could be a comparatively easy first application of the research.
Skies go black in Africa’s worst locust swarms in decades
Leslie Vosshall, head of Rockefeller University’s Laboratory of Neurogenetics and Behaviour, said perhaps the most exciting application would be finding a chemical that would block reception of 4VA.
“The discovery of such a molecule might provide a chemical antidote to insect aggregation and cause locusts to ‘stand down’ and return to their peaceful, solitary way of life,” she wrote in a review commissioned by Nature.
Vosshall pointed out that there are still several unknowns, including whether 4VA is the only thing that causes swarm formation, and whether other locust species respond similarly to the compound.
Kang said genetic modification of locusts might offer “sustainable and green control” but acknowledged such a project would require large-scale and long-term efforts.
“This is an approach for long-term control of locusts, and needs strict biological security evaluation before application.”
Additional reporting by Reuters



Why locusts swarm: scientists identify scent that could be used as weapon against plagues

A swarm of desert locusts in Kenya. File photo: Reuters

An adult male of the locust species Locusta migratoria is seen in a laboratory setting in Beijing, China July 1, 2020. Picture taken July 1, 2020. Le Kang/Handout via REUTERS. NO RESALES. NO ARCHIVES. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY.

Battered by coronavirus and swine fever, is China ready for locusts?

Locusts have ravaged crops in Pakistan, India and East Africa – and now Beijing is sensing a threat to China. Photo: Reuters

FILE PHOTO: A desert locust is seen feeding on a plantation in a grazing land on the outskirt of Dusamareb in Galmudug region, Somalia December 22, 2019. REUTERS/Feisal Omar/File Photo

China’s green zombie fungus could hold key to fighting East Africa’s swarms of locusts

Young locusts in Somalia, where the fungus will be used to try to kill them. Photo: AP

Swarms of locusts land and feed on shea trees, which are a big source of food and income for local farmers, in Otuke on February 17, 2020. - Locust swarms have slowly been arriving into northern Uganda from neighbouring Kenya, threatening the livelihoods of local farmers and cattle herders. Government forces have been mapping out the swarms and spraying them with insecticides, however the real worry will be if these swarms lay eggs that will eventually hatch and spread. (Photo by SUMY SADURNI / AFP)

A locust being eaten inside out by the Metarhizium fungi. Credit: Chinese Academy of Sciences and the University of Maryland

Amid the threat of coronavirus, new swarm of billions of locusts threatens millions in Africa

A swarm of desert locusts flies in Kipsing, near Oldonyiro, in Isiolo county, Kenya. Photo: FAO via AP

In this photo taken Tuesday, March 31, 2020, a motorcyclist rides through a swarm of desert locusts in Kipsing, near Oldonyiro, in Isiolo county, Kenya. Weeks before the coronavirus spread through much of the world, parts of Africa were already threatened by another kind of plague, the biggest locust outbreak some countries had seen in 70 years, and now the second wave of the voracious insects, some 20 times the size of the first, is arriving. (Sven Torfinn/FAO via AP) MANDATORY CREDIT

In this photo taken Wednesday, April 1, 2020, desert locusts sit on vegetation in Kipsing, near Oldonyiro, in Isiolo county, Kenya. Weeks before the coronavirus spread through much of the world, parts of Africa were already threatened by another kind of plague, the biggest locust outbreak some countries had seen in 70 years, and now the second wave of the voracious insects, some 20 times the size of the first, is arriving. (Sven Torfinn/FAO via AP) MANDATORY CREDIT

Plague fears as massive East Africa locust outbreak spreads

A ranger is surrounded by desert locusts as he and a ground team relay the coordinates of the swarm to a plane spraying pesticides, in Nasuulu Conservancy, northern Kenya. Photo: AP

Swarms of desert locusts fly up into the air from crops in Katitika village, Kitui county, Kenya Friday, Jan. 24, 2020. Desert locusts have swarmed into Kenya by the hundreds of millions from Somalia and Ethiopia, countries that haven't seen such numbers in a quarter-century, destroying farmland and threatening an already vulnerable region. (AP Photo/Ben Curtis)

In this photo taken Tuesday, Feb. 4, 2020, pest-control sprayers demonstrate their work on the thorny bushes in the desert that is the breeding ground of desert locusts for a visiting delegation of Somali ministry officials and experts from the Food and Agriculture Organization (FAO), in the desert near Garowe, in the semi-autonomous Puntland region of Somalia. The desert locusts in this arid patch of northern Somalia look less ominous than the billion-member swarms infesting East Africa, but the hopping young locusts are the next wave in the outbreak that threatens more than 10 million people across the region with a severe hunger crisis. (AP Photo/Ben Curtis)

A plane conducting the aerial spraying of pesticides, flies over a swarm of desert locusts in Lemasulani village, Samburu County, Kenya January 17, 2020. Picture taken January 17, 2020. REUTERS/Njeri Mwangi

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Scientists identify chemical compound released by locusts that causes them to swarm
Discovery opens door to possible new ways to prevent the insects from devouring crops



Discovery opens door to possible new ways to prevent swarms of locusts from devouring crops vital to human sustenance as they have for millennia.


Food and agriculture

Africa

Why locusts swarm: scientists identify scent that could be used as weapon against plagues

Scientists identify chemical compound released by locusts that causes them to swarm Discovery opens door to possible new ways to prevent the insects from devouring crops

Scientists identify chemical compound released by locusts that causes them to swarm

Discovery opens door to possible new ways to prevent the insects from devouring crops