Scientists have identified a chemical compound released by locusts that causes them to swarm.
The pheromone – a chemical produced by an animal that affects the behaviour of others of its own species – is released by the migratory locust, or Locusta migratoria.
Called 4-vinylanisole (4VA), it is primarily released from the hind legs and is detected by the antennae of other locusts and sensed by odour receptors.
Now the unique perfume has been identified, a synthetic version of the chemical could be developed to lure locusts into traps to be killed, scientists claim.
Locusta migratoria is the world’s most widespread locust species, which devastates crops made for human consumption in a relentless drive to eat and reproduce.
The UN has called recent locust swarms faced in East Africa ‘unprecedented in modern times’ and ‘a scourge of biblical proportions’.
Record numbers of locusts have descended in devastating swarms across parts of Africa and Asia this year
The insects can devour the same amount of food in a day as approximately 35,000 people in the region, while attempts to control the current plague in East Africa are expected to cost $138 million.
‘In human history, locust plagues, drought and flood were considered as three major natural disasters which caused serious agricultural and economic losses all over the world,’ said research leader Le Kang at the Chinese Academy of Sciences’ Institute of Zoology.
‘As the most widely distributed and one of the most dangerous locust species, the migratory locust represents a serious threat to agriculture worldwide.’
The species is found in grasslands throughout Africa, most of Eurasia south of the Taiga, the East Indies, tropical Australia, and New Zealand.
It differs from the desert locust (Schistocerca gregaria), which inhabits dry grasslands and deserts and has been causing devastation in East Africa this year.
Individually, locusts are not particularly harmful, but they are hugely destructive when they form swarms
Migratory locusts attack pastures and critical crops such as wheat, rice, corn, millet, barley, oats, sugarcane and sorghum.
Swarms can include billions of locusts and span hundreds of square miles as the insects voraciously consume crops.
The chemical insecticides currently used to suppress locust outbreaks raise concerns about human health and safety, but the identification of 4VA could inspire new methods.
The 4VA molecule is released by gregarious migratory locusts and acts as a powerful attractant to migratory locusts.
Locusta migratoria (pictured) is found in grasslands throughout Africa, most of Eurasia south of the taiga, the East Indies, tropical Australia, and New Zealand
Both solitary and gregarious locusts – those that live in groups – are strongly attracted to 4VA, regardless of their age and sex.
If four or five solitary locusts are housed together, they too begin to produce and emit the pheromone.
This then causes swarming behaviour by attracting other locusts in the field, eventually building up a fearsome locust cloud.
And the more that locusts flock together, the more 4VA is emitted.
The pheromone is detected by specific sensory cells, called basiconic sensilla, which are found in the locusts’ antennae.
Here, the molecule binds to a specific olfactory receptor, called OR35, and locusts engineered to lack this receptor are less attracted to 4VA.
A man chases away locusts that were roosting in trees in Kenya in May. East Africa has endured a string of disasters of near-Biblical proportions in 2020
In outdoor tests on artificial turf, sticky traps baited with 4VA snared dozens of locusts released from the lab.
The flat panels, to which an adhesive substance was applied, also caught locusts when deployed in a wetland reserve near Tianjin, eastern China.
The identification of 4VA is a promising development in finding new ways to kill the pests.
Other than synthetic chemicals that lure locusts to their death, other potential techniques could include a chemical that would block 4VA’s effects to prevent swarming.
Locusts that have been genetically modified not to respond to 4VA could also be developed and released to establish wild non-swarming populations, although this would be ‘subject to biosecurity evaluation’, Kang said.
Further research is needed on whether 4VA exists in other locust species such as the desert locust that currently is ravaging parts of Africa and the Middle East.
The study has been published in the journal Nature.
EAST AFRICA’S CATASTROPHIC LOCUST SWARM
The locusts are the next wave in the outbreak that threatens more than 10 million people across the region with a severe hunger crisis
East Africa faced its worst locust plague in 70 years this year.
Since the swarm spawned on the Ethiopia-Somalia border, the pests flew a path of destruction through Kenya, Djibouti, Eritrea, Tanzania, Sudan.
Their number has ballooned into the billions which has left governments scrambling to stop them laying waste to crops.
Around 2,000 of the desert locusts were spotted in the Eastern Equatorial state of South Sudan, the agriculture minister Onyoti Adigo said.
The potentially devastating effects of the grass-guzzling insects was spelled out by the country’s UN representative Meshack Malo.
After reaching South Sudan, authorities feared the outbreak would compound starvation in the war-torn nation.
Experts have warned the main March-to-May cropping season is at risk as eggs laid along the locusts’ path are due to hatch and create a second wave of the insects in key agricultural areas.
The locusts have travelled in swarms the size of Moscow and it has been said the only effective control is aerial spraying with pesticides.