Scientists pinpoint the pheromone that causes locusts to swarm
Taken as individuals, locusts are largely harmless insects much like ordinary grasshoppers, but when gathered together in their notorious swarms they can cause all kinds of environmental destruction. Scientists in China have now identified a key chemical that promotes the formation of these devastating clusters, opening up new possibilities when it comes to controlling their behavior and limiting the damage they cause.
The research focuses on the migratory locust, the most widespread species and one that can begin life as a peaceful, solitary creature. But when they experience changes in environmental conditions, such as a lot of rainfall or moisture, they can enter a gregarious phase, in which they are strongly attracted to other locusts and band together to form swarms of billions that cover vast areas.
As these gigantic clusters migrate through the landscape, they mercilessly strip crops of their grains and utterly devastate farmlands, with studies showing that the economic burden of this is largely carried by subsistence farmers in vulnerable regions. This was most recently seen in Africa this year, where swarms the size of major cities are tearing through crops in the worst locust outbreak the region has seen for decades.
Some interesting biological transformations take place when locusts leave their solitary phase for this gregarious phase. Pigmentation changes see them go from green in color to black, and they begin to produce a molecule that can be metabolized into cyanide, according to Rockefeller University’s Leslie B. Vosshall, who was not involved in the research but wrote a commentary on the discovery in Nature.
Researchers have believed that somewhere along the way, a pheromone that promotes swarming also becomes a part of this mix of changes, but have been unable to confirm the compound so far. Now, scientists at the Chinese Academy of Sciences have done exactly that through a range of field experiments, behavioral assays, electrophysiological recording and olfactory receptor characterization.
The compound in question is known as 4-Vinylanisole, and the team found that both gregarious and solitary locusts, of all ages and sexes, were strongly attracted to it. Interestingly, the team found through its experiments that it took a group of only four or five solitary locusts to come together to kick off production of the aggregation pheromone, and the snowball effect that leads to giant swarms.
Through its investigations, the team pinpointed an odorant receptor called OR35 on the locusts that was strongly activated by 4-Vinylanisole. The researchers even used CRISPR-Cas9 gene editing to engineer mutant locusts that were missing the gene that encodes for OR35, and found that they were unable to detect the pheromone and therefore didn’t respond to it.
“This finding is exciting, because it indicates that a locust can be engineered to be immune to the effects of the pheromone,” writes Vosshall.
Further work is needed to understand where exactly 4-Vinylanisole comes into play in the gregarious phase of the locusts, and what role it plays in their destructive behaviors. But the research opens up some exciting possibilities, including the exploration of compounds that could block the OR35 receptor as a way of preventing the formation of vast locust swarms.
The research was published in the journal Nature, while Vosshall’s commentary is available at the source link below.