Locusts are usually harmless loners. But in a mass, they become plagues. A swarm can contain hundreds of millions of locusts! These hordes can cross continents, eating through crops along the way. A new study has now found what may make a single locust decide to turn social.

Groups of locusts pump out a chemical, scientists now find. And it might explain how individuals of one locust species go from loners to crowd-lovers. The finding might also help scientists develop new ways of controlling or breaking up locust swarms. They might even be able to use those scents to bait the insects into traps.

When solitary locusts get together, they do more than hang out. They transform into what scientists call their “gregarious” form. That’s a fancy word for social. A gregarious locust is a larger, hungrier locust than before. And gregarious groups tend to grow bigger and bigger.

A swarm of desert locusts (Schistocerca gregaria) the size of the city of Rome eats as much food in a day as 51 million people. That’s the entire population of Kenya. This year, East Africa is experiencing its worst locust plague in decades.

Scientists weren’t sure what coaxed solitary migratory locusts of another species, Locusta migratoria, to congregate. But they suspected it might be chemicals known as aggregation pheromones (FAIR-uh-moans). Released by the insects, these airborne scents could act as an beacon. They could summon other locusts to morph into a gregarious swarm.

Le Kang is an an entomologist, someone who studies insects. He and his colleagues at the Chinese Academy of Sciences in Beijing scouted for aggregation pheromones. They started by identifying chemicals that gregarious locusts pump out. The team puffed six of these scents into arenas with lone locusts. They also tested control scents — those not made by gregarious locusts. The goal was to see if any of the six scents attracted the insects. One did. Called 4VA (for 4-vinylanisole), it drew in locusts of all sexes and ages, whether solitary or gregarious.

That’s important, says Baldwyn Torto, who was not involved in the study. As a chemical ecologist, he studies chemical interactions between organisms and their environment. He works at the International Centre of Insect Physiology and Ecology in Nairobi, Kenya. Attracting both loner and gregarious locusts, he says, means 4VA could function to both bring solitary locusts into the swarm and keep that swarm together over time.

Solitary locusts start spewing 4VA once they gather in groups as small as four or five, Kang found. As group size grows, 4VA levels rise. That could broadcast a larger signal and contribute to an exponential growth, leading to swarms. 

Kang and his colleagues also confirmed 4VA can attract locusts in the real world. To test this, they baited sticky traps with the chemical and put them on artificial grass and a natural breeding area of migratory locusts in northern China. Traps with 4VA attracted more locusts than did traps without the pheromone. The effect was small, here. But the researchers tested the traps only on locusts a short distance away.

“It’s a significant and exciting study,” says Torto. “This [compound] has potential.” But while 4VA is clearly a player, he notes, it may not be the whole story.

Chemical communication among insects isn’t always controlled by a single pheromone. Multiple compounds often work together. And this study didn’t look into that. He says there’s a chance that other odors of gregarious locusts could interact with 4VA. The combo might make intensify the call to turn social.

Still, the prospect of baited traps for locust control excites Torto. “We don’t have a good way of attracting locusts,” he says. Many regions manage outbreaks by dumping pesticides onto swarms from planes. This chemical dump can harm livestock and the environment. Traps laced with 4VA could concentrate locusts. When they’re all in one place, killing them might become easier. Such baits would be especially helpful if they attract other types of locusts, too, like the desert species.

This study also could help scientists change the locusts themselves. Kang and his colleagues identified the locust’s protein that detects 4VA. It’s nestled on specific sensory hairs that extend from the insect’s antennae.

A gene-editing tool known as CRISPR/Cas9 lets scientists tweak an organism’s DNA. Using CRISPR, Kang and his colleges were able to change locust DNA so that the insects no longer made a 4VA detector. Without it, the chemical no longer lured in the locusts.

A chemical that blocks antennae from sensing 4VA could be sprayed on locusts to prevent swarming, the researchers suggest. Or, scientists could engineer locusts so they don’t make the 4VA sensor. Such locusts would be less likely to swarm.

Any research that offers new ways to manage pests without poisons is very exciting, says Arianne Cease. She studies sustainability — how to use resources so they are available in the future — at Arizona State University in Tempe. Such technologies are still a ways off. CRISPR might have off-target effects, such as editing DNA that scientists don’t want to change.

Changing the DNA of a species might also change locusts in ways scientists don’t yet understand. Changes to a locusts’ genes would get passed on to any offspring. That might make any harmful changes permanent. People affected by locust swarms would need to weigh issues like these, before anyone edits wild-locust DNA.

Cease also questions whether turning off one gene would prevent swarms. Becoming a swarm involves a whole set of changes. Locusts change their behavior, body function and body size. Tweaking just one aspect of this may not prevent swarming, she says. “I’d be surprised if there were just one smoking gun.”

aggressive: (n. aggressiveness) Quick to fight or argue, or forceful in making efforts to succeed or win.

behavior: The way something, often a person or other organism, acts towards others, or conducts itself.

chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

compound: (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.

CRISPR: An abbreviation — pronounced crisper — for the term “clustered regularly interspaced short palindromic repeats.” These are pieces of RNA, an information-carrying molecule. They can guide an enzyme, called Cas9, to cut through genetic material like a scissors. In this way, they can edit — or alter — specific genes so that they can then study how those genes works, repair damage to broken genes, insert new genes or disable harmful ones.

crop: (in agriculture) A type of plant grown intentionally grown and nurtured by farmers, such as corn, coffee or tomatoes. Or the term could apply to the part of the plant harvested and sold by farmers. 

DNA: (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

ecology:  A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

engineer: A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need. (v.) To perform these tasks, or the name for a person who performs such tasks.

environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

exponential: A trend or number that grows dramatically. The increase does not occur at a steady pace. Instead, it rises at an increasing rate.

gene: (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

genetic: Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

insect: A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.

livestock: Animals raised for meat or dairy products, including cattle, sheep, goats, pigs, chickens and geese.

migratory: An adjective for species that travel long distances each year, along fairly regular paths, to to find food or more hospitable conditions (such as better weather). Such travels are known as migrations.

organism: Any living thing, from elephants and plants to bacteria and other types of single-celled life.

outbreak: The sudden emergence of disease in a population of people or animals. The term may also be applied to the sudden emergence of devastating natural phenomena, such as earthquakes or tornadoes.

pheromone: A molecule or specific mix of molecules that makes other members of the same species change their behavior or development. Pheromones drift through the air and send messages to other animals, saying such things as “danger” or “I’m looking for a mate.”

physiology: The branch of biology that deals with the everyday functions of living organisms and how their parts function. Scientists who work in this field are known as physiologists.

plague: (noun) Any horrific infection that spreads easily and kills many people, usually quickly. Or any catastrophic event that causes destruction that can lead to sickness or death (such as a crop-destroying plague of locusts).

population: (in biology) A group of individuals from the same species that lives in the same area.

protein: A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

sustainability: (adj: sustainable) To use resources in a way that they will continue to be available in the future.

swarm: A large number of animals that have amassed and now move together. People sometimes use the term to refer to huge numbers of honeybees leaving a hive.

technology: The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

Journal:​ ​​ X. Gao et al. 4-Vinylanisole is an aggregation pheromone in locusts. Nature. Published online August 12, 2020. doi: 10.1038/s41586-020-2610-4.

Jonathan Lambert is the staff writer for biological sciences, covering everything from the origin of species to microbial ecology. He has a master’s degree in evolutionary biology from Cornell University.

Founded in 2003, Science News for Students is a free, award-winning online publication dedicated to providing age-appropriate science news to learners, parents and educators. The publication, as well as Science News magazine, are published by the Society for Science & the Public, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education.


Locust, Swarm behaviour, Chemistry, Research, Desert locust

World news – GB – A single chemical may draw lonely locusts into a hungry swarm

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