An irresistible scent makes locusts swarm, study finds

TOKYO: The coronavirus isn´t the only plague making headlines this year — locusts are devastating crops in several parts of the world, and now scientists are discovering why the pest forms destructive swarms. On its own, a locust is fairly harmless. But so-called solitary locusts can undergo a metamorphosis, changing colour and joining together with millions of others in catastrophic clouds that strip fields. So what prompts locusts to transform from solitary to “gregarious”?

A study published Wednesday in the journal Nature reveals the secret lies in a pheromone. Almost like an irresistible perfume, the chemical compound is emitted by locusts when they find themselves in proximity to just a few others of their kind. The chemical attracts other locusts, who join the group and also begin emitting the scent, creating a feedback loop that results in enormous swarms. The discovery offers several tantalising possibilities, including genetically engineering locusts without the receptors that detect the swarming pheromone, or weaponising the pheromone to attract and trap the insects. The study comes as record numbers of locusts devour crops in east Africa and threaten the food supply in Pakistan. It focused on the migratory locust, the most widely distributed species of the insect, and examined several compounds produced by the bug. It found that one in particular — 4-vinylanisole, or 4VA — appeared to attract locusts when emitted, and that the more locusts flocked together, the more 4VA they emitted.