The diamondback moth, Plutella xylostella is a cosmopolitan pest that has evolved resistance to
all classes of insecticide, and costs the world economy an estimated US $4-5 billion annually.
We analyse patterns of variation among 532 P. xylostella genomes, representing a worldwide
sample of 114 populations. We find evidence that suggests South America is the geographical
area of origin of this species, challenging earlier hypotheses of an Old-World origin. Our
analysis indicates that Plutella xylostella has experienced three major expansions across the
world, mainly facilitated by European colonization and global trade. We identify genomic signatures
of selection in genes related to metabolic and signaling pathways that could be evidence
of environmental adaptation. This evolutionary history of P. xylostella provides insights
into transoceanic movements that have enabled it to become a worldwide pest.