Ancient trans-Atlantic flight explains locust biogeography: molecular phylogenetics ofSchistocerca

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Abstract
The desert locust (Schistocerca gregaria) has been an important agricultural pest at least since biblical times. Although the ecology, physiology and behaviour of this insect species have been well characterized, its biogeographical origins and evolutionary history are more obscure.Schistocerca gregariaoccurs throughout Africa, the Middle East and Western Asia, but all other species in the genusSchistocercaare found in the New World. BecauseS. gregariahas the capacity for extreme long-distance movement associated with swarming behaviour, dispersal may have played an important role in determining current distribution patterns. Some authors have argued thatS. gregariais the product of an eastward trans-Atlantic dispersal from North America to Africa; others consider it more likely that the New World taxa are the product of westward dispersal from Africa. Here, we present a mitochondrial DNA phylogeny ofSchistocercaspecies that supports the monophyly of New World species (including the Galapagos endemicHalmenus) relative toS. gregaria. In concert with observed patterns of molecular divergence, and in contrast to previous morphological studies, our analysis indicates a single trans-Atlantic flight from Africa to South America, followed by extensive speciation and ecological divergence in the New World.