Blocking a pheromone stops locusts from swarming

Two key enzymes reveal how migratory locusts produce their ‘swarm pheromone’ in their hind legs – and how that production can be shut down.

Chinese researchers have suppressed the swarming behaviour of migratory locusts by blocking the synthesis of the pheromone responsible for their mutual attraction. In Nature of 25 June, the biochemists first partly unravel the biosynthesis of the pheromone, then identify enzyme inhibitors that shut down its production. The strategy could potentially help reduce the heavy pesticide use associated with locust plagues, which regularly devastate harvests across Africa and Asia.

Migratory locusts (Locusta migratoria) switch between two behavioural states depending on their environment: a solitary phase in which they avoid conspecifics, and a gregarious or ‘swarming’ phase in which they mass together. This switch is driven partly by touch, but also by smell. One of the most important signalling compounds involved is 4-vinylanisole (4VA), a volatile compound that has been known since 2020 to enhance mutual attraction. By comparing hungry and recently fed locusts, the researchers established that 4VA production is linked to food intake: the insects convert the amino acid phenylalanine, derived from their plant-based diet, stepwise into the pheromone through a series of chemical reactions.

Schematic representation of the biosynthesis (and possible intervention, top right) of the swarm pheromone 4-vinylanisole (4VA). Illustration: Kang Le Lab, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.

Because locusts in the gregarious phase secrete 4VA primarily through their hind legs, the researchers collected and analysed RNA from the hind legs of swarming individuals and compared gene expression patterns with those of solitary conspecifics. This allowed them to identify two enzymes active in the production of 4VA: 4VPMT1 and 4VPMT2, both belonging to the methyltransferase family – enzymes that add methyl groups and thereby shape odorant molecules. In locusts in which these enzymes were switched off, 4VA production almost completely ceased and swarming behaviour did not occur.

This is not, however, a realistic option for large-scale application in the field. The biochemists therefore determined the three-dimensional structure of 4VPMT2 using X-ray crystallography, and then screened thousands of small molecules for their ability to block the enzyme. The organic compound 4-nitrophenol bound most effectively and inhibited enzyme activity almost completely.

Starting point
The compound itself is environmentally harmful, but serves as a starting point for identifying more benign variants. Several inhibitors, when administered via food, proved capable of reducing 4VA production in living locusts by 80 per cent. In behavioural experiments, swarming locusts consequently lost their mutual attraction, whilst solitary locusts no longer switched to group formation.

‘This is unquestionably an elegant study, which gives us a little more insight into one part of this highly complex process’, says Jozef Vanden Broeck, a locust expert at KU Leuven. ‘But this particular subprocess is presumably species-specific: there are several species of migratory locust and they are not very closely related to one another. The mechanisms leading to swarming behaviour may have evolved independently multiple times among them – including in the far more destructive desert locust. I also wonder how these enzyme inhibitors could ultimately be deployed safely and efficiently under field conditions to reverse the behaviour of those enormous travelling swarms. This study offers hope, but a practical solution is not yet immediately at hand.’

See also:
–Agencies race to prevent new food crisis as (desert) locusts return to northern Africa – Mongabay, 3 July 2025
–Locust Watch – FAO portal with forecasts and early warnings on desert locusts