Plagues of Locusts Could Be Eradicated After Swarming Pheromone Discovered

A pheromone that could be used to stop locusts from swarming has been discovered by scientists, potentially helping save millions of people from risk of food shortages. Researchers have identified a powerful molecule released by migratory locusts that serves as a powerful attractor to others, regardless of sex or age.

By harnessing this molecule, scientists say they could develop new methods to stop locusts from swarming. It could also be used to attract swarms where they could be trapped and killed.

This year has seen a record number of locust swarms across East Africa and southwest Asia, devastating local agriculture and prompting a warning from the United Nations that millions are at risk of food insecurity.

These swarms have been linked to climate change. Research suggests hotter temperatures are linked to more damaging locust swarms. Wetter weather also helps locusts to multiply, and climate change is believed to be behind an abnormal amount of rainfall recorded at the end of 2019, potentially explaining this year's devastating swarms.

Locusts are normally solitary creatures, but under certain environmental conditions, they switch to a "gregarious phase." In this phase, they change color, move faster and are attracted to one another, leading to the creation of swarms.

Locust swarms can be made up of billions of individuals. Each locust can consume its own weight in vegetation each day. This means as they sweep through, they can destroy crops over vast areas, leaving little to none for people in regions affected. At present, control measures include chemical pesticides and biopesticides, along with ground control operations.

In a study published in Nature, scientists from the Chinese Academy of Sciences looked at what causes migratory locusts to be attracted to one another. It had long been thought a pheromone may be behind the swarming behavior, but until now no good candidate had been identified.

The team looked at 35 compounds emitted by locusts, six of which were found in gregarious locusts, but not solitary ones. From these, they found one that was highly potent, attracting males and females, juveniles and adults. The concentration of the pheromone, 4-vinylanisole, in the air was found to be significantly increased when the number of locusts in a region rose.

When a handful of solitary locusts were put together, they were found to produce and emit the pheromone. When locusts were engineered to lack a receptor, OR35, that the molecule binds to, they were less attracted to 4-vinylanisole.

Farmers in Pakistan's southern Sindh province trying to disperse a swarm of locusts on July 1, 2020. Scientists in China have discovered the pheromone that makes these insects swarm. SHAHID ALI/AFP via Getty Images

The researchers say the findings present a number of options for controlling locusts with this pheromone. A synthetic version could be used to attract and trap swarms in the wild—something the team had success with in field experiments.

Gene editing could also be used to introduce a "mutant" population that was not attracted to the pheromone. These could be released into the wild in a bid to provide long-term population management—over time, the mutation would enter the wider population, making the species less likely to be affected by the pheromone. Another idea is to create a chemical that blocks the activity of the molecule, which would stop the locusts from aggregating.

"Further research is needed to test the feasibility of these and other related strategies," the team wrote.

In a related News & Views article for Nature, Leslie B. Vosshall, from the Kavli Neural Systems Institute and the Howard Hughes Medical Institute at the Rockefeller University, New York, said a number of important questions remain unanswered. This includes whether the pheromone is solely responsible for the swarming behavior. However, the potential applications, she said, are plentiful.

"Most exciting is the possibility of using OR35 as a tool to identify compounds that block the activity of this receptor," she wrote. "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."