Cannibalism drives vast locust swarms, says study

May 9th, 2008 - 1:55 pm ICT by admin  

Washington, May 9 (IANS) Cannibalism, spurred by sheer hunger, drives billions of tiny locusts to take to flight, whose movement blacks out the sun and the skies for tens of kilometres. Long puzzled by the phenomenon, a team from universities of Oxford and Sydney, led by Iain Couzin of Princeton, set out to find answers and now seem to have solved the enduring mystery.

“Cannibalism,” said Couzin, “is rife within marching bands of locusts.” Desert locusts usually feed on vegetation, but individual locusts have been observed to feed on other locusts, live or dead.

“No one knew until now that cannibalistic interactions are directly responsible for the collective motion exhibited by these bands,” added Couzin, whose student, Sepideh Bazazi, is a co-author of the paper.

Dwindling food supplies compel young locusts to eat others of their kind. Starved of essential nutrients like protein and salt, young locust “nymphs” will nip at each other. Those under siege react by running from the aggressors.

Others become jittery and simply flee locusts approaching them from behind. That’s how one aggressive interaction can lead to another and prompt vast migration, Couzin said.

As the activity intensifies, with all the biting and ominous approach of others, it drives the momentum of individual locusts forward.

The researchers reached the conclusion by studying immature, flightless locusts. They developed computerised motion analysis to automatically track the insects marching in an enclosed arena.

In nature, Couzin said, these locust nymphs can gather in large mobile groups called bands. They can stretch over tens of kilometres, devouring vegetation as they march. They inevitably precede the flying swarms of adult locusts.

“Once they take flight, locust control is extremely expensive and ineffective,” Couzin said. “So understanding when, where and why the bands of juvenile locusts form is crucial for controlling locust populations.”

Throughout history, locusts have invaded up to one-fifth of the earth’s surface, he said. They have contributed to major humanitarian crises in areas such as Darfur and Niger.

These findings have appeared in Thursday’s online edition of Current Biology.

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