for National Geographic News
Somewhere between three to five million years ago a giant swarm of locusts left West Africa and flew across the Atlantic Ocean to colonize the New World, a new study shows.
Using DNA evidence, researchers have reconstructed the evolutionary relationships among insects of the genus Schistocerca, a diverse group of locust species found throughout the Americas, Africa, and Asia.
"Our results show that the first Schistocerca species to evolve was the African desert locust," said Nathan Lovejoy, an assistant professor at the University of Toronto at Scarborough in Canada.
"This suggests that Schistocerca originated in Africa and somehow dispersed across the Atlantic."
How the locusts made that trans-Atlantic journey remains a mystery, however, since the insects can't store enough fat to power a trip that would last several days.
A single African desert locust (Schistocerca gregaria) is harmless to humans. But when the insects congregate in one place where food is abundant, their look and social behavior alters in a phenomenon known as phase change.
Phase change causes the locusts to swarm over vegetation, behavior that has wreaked havoc on crops in Africa and the Middle East for centuries.
A 2004 locust outbreak in West Africa caused significant crop losses, contributing to a food shortage in Niger earlier this year. (Read "Food Crisis In Niger Will Strike Again, Experts Say.")
Scientists studying this economically infamous insect have long wondered why the closest relatives of the desert locust are found in the Americas and not in Africa.
A 2004 study led by Hojun Song, a graduate student at Ohio State University, used locust anatomy to reconstruct the evolutionary history of the insects. Song's work suggested that the desert locust colonized Africa from North America.
Lovejoy and his colleagues used DNA sequences from 20 Schistocera species to make a similar reconstruction. The National Geographic Society and the National Science Foundation funded the team's work.
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