Recent range expansion of the maize weevil Sitophilus zeamais

Insects and insect remains, especially of stored grain insects, are important sources of information for human history in a variety of contexts. Grain weevils of the genus Sitophilus, and particularly the granary weevil (S. granarius (L.)), are frequent presence in archeological sites and have been important in tracing past urban environments, grain origin and dispersion, routes of grain trade, and history of storage. Much less is known about the other two related grain weevil species, the rice weevil (S. oryzae (L.)) and the maize weevil (S. zeamais Motschulsky), whose natural history is a matter of controversy despite their importance as insect pests of stored cereals. Here we examined the phylogeographic structure of the maize weevil by sampling two mitochondrial gene sequences (COI and COII), ribosomal nuclear region fragments (ITS1, 5.8S and ITS2), and eight microsatellite markers throughout the species` range and exploring its evolutionary history. Our findings suggest a recent spatial expansion of maize weevil. However, it was not possible to draw assumptions about the historical dispersion of the maize weevil in Brazil and the world, probably because the populations of this species are derived from multiple and constant migration events. The microsatellite data showed moderate population divergence among the sampling sites, and low divergence between the sampling sites within the same group, which confirms the presence of gene flow among crops and storage grain sites.