An ancient plague of locusts returns
For the first time in 15 years, enormous swarms of desert locusts (Schistocerca gregaria) have hit Africa and Asia, particularly affecting Ethiopia, Kenya, Somalia, India and Yemen.
So these countries are fighting two devastating plagues at once – SARS-Coronavirus-2 and locusts.
Mentioned in the Koran and the Bible and depicted on ancient Egyptian tombs, locusts have plagued the people of Asia, the Middle East and Africa on and off for millennia, ravaging crops and causing famine.
Locusts are short-horned grasshoppers that usually live a solitary life. But they are distinguished from their grasshopper relatives by the ability to transform into gregarious, swarming locusts. When this change occurs, usually triggered by adverse weather conditions, the insects breed rapidly and form huge swarms typically containing 4-8 billion locusts.
Devour
Moving speedily over long distances they devour vast quantities of vegetation, every day consuming the equivalent of the daily food ration for around 3.5 million people.
Present day locust control mainly consists of spraying insecticides from planes, but this is inadequate for the task and detrimental to other more kindly insects.
Why and how benign, solitary grasshoppers turn into gregarious, swarming locusts is not known and despite threatening the lives of around 20 million people, research on the subject has been minimal. Fortunately, this has recently changed and researchers have made significant progress in understanding how these insects periodically become gregarious*.
The scientists isolated 35 compounds produced by migratory locusts and identified one among them, a pheromone called 4-vinylanisole (4VA), as particularly interesting.
When they crowded groups of 30 locusts into small cages, the insects produced 4VA within 24 hours, and this pheromone strongly attracted other locusts regardless of age or sex, which soon gathered to form a swarm.
Further field trials using sticky boards bearing either 4VA or a control chemical confirmed the pheromone’s specific ability to attract locusts.
This finding now points the way for novel control strategies. If 4VA is used to attract millions of locusts to a specific area, insecticide spraying could be carried out in a controlled and targeted manner.
* Guo, X et al, Nature, 584, p584. 2020. Nature, 584, p497. 2020