Chemical Discovered by Scientists Halts Locust Cannibalism

Plagues of locusts darkening the skies and destroying all things that grow have been recorded since biblical times, and today they threaten the food security of millions of people across Asia and Africa.

But a new discovery announced Thursday — about a pheromone that insects emit to avoid being cannibalized when they’re in a swarm — could pave the way for curbing voracious pests.

Study leader Bill Hanson, director of the Department of Developmental Neuroanatomy at the Max Planck Institute, told AFP that the new paper, which was published in Sciencesbuilt on previous research that found swarms of locusts are directed not by cooperation – but in fact by the threat of being consumed by other locusts.

While cannibalism is repulsive to modern humans, cannibalism is rife in nature—from lions killing and devouring cubs that are not their offspring, to foxes consuming dead relatives for energy.

For locusts, cannibalism is believed to serve an important ecological purpose.

The migratory locust (Locusta migratoria) occurs in different forms and behaves so differently that until recently it was thought to be an entirely different species.

Most of the time, they are in a “solitary” stage, where they keep to themselves and eat relatively little, like shy grasshoppers.

But when the population density increases due to rains and temporarily good breeding conditions, which is followed by a scarcity of food, they undergo major behavioral changes due to a rush of hormones that increase their speed, causing them to gather in swarms and become more aggressive.

This is known as the “gathering” phase and the fear of cannibalism is believed to help keep the swarm moving in the same direction, from an area of ​​lower food concentration to higher, according to 2020 research by Ian Kosin of the Max Planck Institute for Animals. research.

“The grasshoppers eat from behind,” Hanson explained.

“So if you stop moving, the other one will eat you, and that got us thinking almost every animal experiences some kind of countermeasure.”

In painstaking experiments that took four years to complete, Hanson’s team demonstrated for the first time that rates of cannibalism did indeed increase as the number of caged “communal” locusts rose, proving in the laboratory what Cousin had observed in the field in Africa (the starting point was about 50 per cage).

Next, they compared the odors emitted by solitary and communal locusts, finding 17 odors produced exclusively during the social stage.

Among these substances, one chemical, known as phenyl acetonitrile (PAN), was found to repel other grasshoppers in behavioral tests.

PAN participates in the synthesis of a powerful toxin sometimes produced by community locusts – hydrogen cyanide – so the emission of PAN seemed appropriate as a signal to tell others to back off.

Genome editing

To confirm the result, they used CRISPR editing to genetically modify the locusts so that they could no longer produce PAN, which in turn made them more susceptible to cannibalism.

For further confirmation, they tested dozens of locust olfactory receptors, eventually landing on one very sensitive to PAN.

When they modified the locust’s gene to stop producing this receptor, the modified locusts became more cannibals.

In a related commentary in the journal Science, researchers Iain Couzin and Einat Couzin-Fuchs said the discovery helped shed light on the “complex balance” between the mechanisms that cause migratory locusts to swarm together versus compete with each other.

So future approaches to locust control could use technology that helps tip the delicate balance toward more competition, but Hanson cautioned: “You don’t want to wipe out the species.”

He added, “If we can reduce the size of the swarms, and direct them to areas where we do not grow our crops, then a lot can be achieved.”

© 2023 AFP