Among the many crises of 2020 has been some of the worst plagues of locusts on record, which has destroyed crops, livelihoods, and threatened starvation in many parts of the Middle East and Africa. A new discovery, published in the journal Nature, has uncovered which specific pheromone drives locusts to swarm, bringing new hope for a strategy to halt their devastating spread.
Scientists have long suspected that an aggregate pheromone that attracts locusts was responsible for the swarming behavior of these hungry insects. Several pheromones were known to science but precisely which one attracted both males and females in a way significant enough to constitute a swarm had remained a mystery.
The researchers isolated six compounds from a collection of 35 produced by locusts, which were chosen because they are more common in locust species that swarm rather than those that live a solitary life. They tested each of the six pheromones to see how they affected locusts and found that only the molecule 4-vinylanisole was both potent and capable of luring in male and female locusts from all developmental stages. Even more telling was that 4-vinylanisole was also capable of luring in solitary locusts, demonstrating its ability to drive generations of animals into a frenzy.
The concentration of this potent pheromone grew as population density increased, which demonstrates the positive-feedback loop that sees swarm events quickly escalate into plagues of a biblical proportion. Testing its effectiveness on varying group sizes, the researchers discovered that just four or five locusts were needed to launch a 4-vinylanisole-triggered swarming event.
Climate change has seen recent seasons of unusually heavy rains, which have supported a population explosion of the desert locust Schistocerca gregaria. Their swarms have been billions of members strong, leaving ravaged vegetation and crops in their wake. The effect has been such that farmers are losing their livelihoods and vulnerable regions are finding themselves without sufficient food to keep citizens fed.
Currently, the only weapon against such locust plagues is heavy pesticide use but with fast-moving swarms and a host of beneficial insects at risk, the strategy is deeply flawed. It’s hoped that this new understanding of the role of 4-vinylanisole in swarming events can be turned against the locusts in halting the positive-feedback loop. The researchers suggest that a synthetic pheromone could be used to lure swarms into traps or instead a chemical block for 4-vinylanisole could be formulated to stem aggregations before they happen.