The one molecule that turns grasshoppers into locusts.

Science News reveals the one chemical that transforms harmless, solitary insects into a crop-destroying, famine-triggering locust swarm:

Now, scientists have pinpointed a compound emitted by congregating locusts that might explain how individuals of one widespread species overcome their innate aversion to socializing. The finding, described August 12 in Nature, could inform new ways of controlling or preventing locust swarms, potentially by attracting the insects with their own scents.

“It’s a significant and exciting study,” says Baldwyn Torto, a chemical ecologist at the International Centre of Insect Physiology and Ecology in Nairobi, Kenya who wasn’t involved in the study. “We don’t have great ways of baiting locusts. This [compound] has potential.”

Scientists weren’t sure what coaxes solitary migratory locusts (Locusta migratoria) to congregate, but suspected what are known as aggregation pheromones.

Le Kang, an entomologist at the Chinese Academy of Sciences in Beijing, and colleagues began their search for aggregation pheromones by identifying compounds emitted only by gregarious locusts. The team puffed six of these gregarious-only scents into arenas along with control scents to test whether any acted as attractants for solitary locusts. One compound, 4-vinylanisole, or 4VA, did the trick. It proved alluring to locusts of all sexes and ages, including both solitary and gregarious forms.

That’s crucial, Torto says, because it demonstrates that 4VA could function to both bring solitary locusts into the fold of the swarm, as well as maintain a swarm’s cohesiveness over time.

Gregarious locusts start emitting 4VA once they gather in groups as small as four or five individuals, Kang found. As group size grows, 4VA concentration shoots up, potentially broadcasting a larger signal and contributing to the exponential growth of swarms.

Traps laced with 4VA could concentrate locusts and make treatment with insecticides or pathogens much easier, especially if 4VA acts as an attractant in other species as well, like the desert locust. Currently, many regions manage outbreaks by dumping pesticides on