Using genetic evidence from more than 20 species of locusts, scientists from the Universities of Toronto, Arizona, Maryland, Cornell University and the U.S. Department of Agriculture have answered a long-standing conundrum: why are the closest relatives of the African desert locust (Schistocerca gregaria) found in the New World, rather than Africa? The desert locust is one of the world's most economically important insects, and is capable of forming massive swarms that devastate crops.
DNA shows that ancestors of the desert locust flew across the Atlantic and gave rise to a diverse group of New World species. "If we were standing on the coast of Africa, we might have these swarms of locusts heading off across the Atlantic," says Nathan Lovejoy, an assistant professor of in the Department of Life Sciences at the University of Toronto at Scarborough, who led the research along with Sean Mullen, now a postdoctoral researcher at the University of Maryland.
How the locusts made the trans-Atlantic flight is unclear, since the insects don't have enough fat to power a trip lasting several days. "One unlikely hypothesis is that while the locusts were flying across, as their brethren died and landed in the ocean, they formed huge floating mats of dead locusts," says Lovejoy. "The other locusts would land on these mats, rest and feed on the dead bodies, then take off and keep flying." Another possibility is that among the millions of swarming locusts were a few exceptional insects that somehow managed to survive the flight. Lovejoy adds that high-altitude winds would have been essential for the swarm's flight. There is a modern-day example of this phenomenon -- in October 1998, a swarm of desert locusts crossed the Atlantic, travelling from Africa to the Caribbean.
Using muscle samples taken from the powerful hind legs of locusts, Lovejoy and his colleagues used mitochondrial DNA sequences to reconstruct the evolutionary history of the Schistocerca locusts. The team found that the desert locust lineage gave rise to the more than 50 Schistocerca species found in the western hemisphere.