Locust Swarms Switched On by Brain Chemical

Christine Dell'Amore
National Geographic News
January 29, 2009

The social life of a desert locust is a study in extremes: One moment it's an irritable loner, the next it's happily rubbing elbows with huge swarms of its own species.

(See locust swarm pictures.)

What turns this love-hate relationship on and off, a new study says, is a brain chemical common to most animal species—serotonin.

In a recent experiment, scientists found a close connection between how sociable the insects became and the levels of the neurotransmitter in their bodies.

"This really is a new discovery," said study co-author Stephen Rogers of the University of Oxford in the U.K.

"We had a good idea that [locust] behavior changed rapidly, so we did a broad sweep of neurotransmitters and found that serotonin changes in a very narrow window [of time]."

The results may someday lead to strategies for controlling swarms of the critters, which appear every few decades and munch their way through crops in arid lands from West Africa to India.

(Related story: "Cannibal Crickets Cause 'Forced Marches' Through Crops, Study Says" [February 28, 2006].)

Strategy of Desperation

About 90 percent of the time desert locusts live in small numbers scattered across the desert, avoiding as best they can other locusts.

It's only when the insects are forced to crowd together that they take on a swarm mentality.

Locusts switch into swarm behavior based on two cues: when they see and smell other locusts for an extended period or when their hind legs are constantly jostled.

Continued on Next Page >>


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