How locusts stop themselves from eating each other

By Stephen Beech via SWNS

Locusts give off a toxic chemical to stop themselves eating each other when they swarm, reveals new research.

Vast clouds of voracious insects take on the proportions of natural disasters and threaten the food supply of millions of people, especially in Africa and Asia.

As the eighth of the 10 biblical plagues, the Book of Exodus in the Old Testament describes how swarms of destructive locusts darkened the sky and ate everything that grew in fields and on trees.

Scientists suspect that cannibalism among locusts contributes to their swarming behavior, and swarms, therefore, constantly move on because individual animals are always on the run from others pursuing them.

Study leader Professor Bill Hansson, of the Max Planck Institute in Germany, explained the starting point of the research.

Prof. Hansson said: "We wondered how these insects influence each other's behavior within huge swarms, and whether olfaction plays a role.

"An important basis for us was the research on the formation of locust swarms by Professor Iain Couzin of the Max Planck Institute for Behavioural Biology in Constance."

He explained that migratory locusts occur in different phases. In the solitary phase, the insects live individually and stay in the area, while in the gregarious phase, they exhibit the typical swarming behavior that fits their denomination as migratory locusts.

Study first author Dr. Hetan Chang, of the Max Planck Institute for Chemical Ecology, said: "In most cases, locusts are in the solitary phase, where they avoid physical contact with conspecifics and eat comparatively little food.

"If the population density increases due to rainfall and sufficient food, the locusts change their behavior within a few hours; they can smell, see, and touch each other.

"These three types of stimulation increase serotonin and dopamine levels in the locust brain, causing solitary locusts to become aggressive gregarious locusts that are very active and have a large appetite.

"They also release aggregation pheromones, which eventually leads to swarming and poses a huge threat to agricultural production.

"Cannibalism does only occur in the gregarious phase."

Behavioral experiments with the migratory locust Locusta migratoria showed that cannibalism rates increased with the number of gregarious animals that were kept together in a cage.

The team said the findings show a direct relationship between population density and cannibalistic behavior.

To find out if gregarious locusts emit particular odors that are not produced in the solitary phase, the researchers analyzed and compared all odors emitted by solitary and gregarious locusts in the juvenile stage.

Of the 17 odors produced exclusively in the gregarious phase, only phenylacetonitrile (PAN) turned out to be an odor signal that deterred other locusts in behavioral tests.

For further confirmation of PAN's function, the research team used genetically modified locusts that could no longer produce PAN.

Dr. Chang said: "We showed that as population density increased, not only did the level of cannibalism rise, but the animals also produced more PAN.

"Using genome editing, we were able to knock out an enzyme responsible for the production of this compound.

"This allowed us to confirm its strong anti-cannibalistic effect because cannibalism was again significantly increased when the animals were no longer able to produce the compound."

The researchers, whose findings were published in the journal Science, said a pheromone that controls cannibalism is an "absolutely new" discovery.

Because cannibalism has a major impact on locust swarm dynamics, they believe a fundamental understanding of the population ecology of the insects, particularly the effect of PAN, opens up new possibilities for locust control.

Prof. Hansson added: "If you inhibit the production of PAN or the function of the receptor, you could get the locusts to behave more cannibalistically and potentially control themselves in that way."