How a pheromone makes locusts swarm

Locusts typically lead solitary lives. But unusually heavy rains, for example, can trigger these grasshoppers to multiply and aggregate into gargantuan swarms that decimate pastures and fields.

For decades, scientists have been trying to understand how and why the locusts turn gregarious and gather by the millions. In 2020, Chinese Academy of Sciences researchers identified a pheromone called 4-vinylanisole(4-VA) released by the insects that lures nearby locusts and recruits them into joining the swarm. In a new study, the same team found that 4-VA promotes such gregarious behavior by increasing social interactions among locusts (Proc. Natl. Acad. Sci. U.S.A. 2023, DOI:10.1073/pnas.2306659120).

Biologist Jing Yang and her colleagues conducted laboratory experiments in cages to observe locust behavior with and without 4-VA. Solitary individuals started becoming social within 24 h of being surrounded by other locusts in the presence of 4-VA, while it took at least 48 h for solitary insects to exhibit those traits in the pheromone’s absence. “As the number of individuals grows and the perception of 4-VA increases, the locusts begin to interact socially,” Yang says. “They learn from each other, imitate each other’s movements, and change their behavioral traits to those of the gregarious phase.”

Her team noted that 4-VA can accelerate the shift to such social behavior, but senior author Xiaojiao Guo adds that other factors may also contribute to induce swarming. A possible way to control locust plagues would be to tinker with their ability to produce 4-VA. “Maybe if we don’t let the locusts produce 4-VA, they won’t aggregate,” she says.