Implications of a phylogeographic approach for the selection of Ceutorhynchus assimilis as a potential biological control agent for Lepidium draba

The root-galling weevil, Ceutorhynchus assimilis Paykull (Coleoptera, Curculionidae), has been selected as one of the candidates to control Lepidium draba L. (Brassicaceae), a highly invasive weed in western North America. Originally been described as oligophagous, also attacking crop species, previous studies indicated that a specific host race to L. draba exists in C. assimilis. We therefore explored the evolutionary history and phylogeographic structure of this weevil by sampling individuals from 67 populations, spanning 12 countries and five different host plant species including L. draba. To explore the genetic diversity of C. assimilis, we analyzed the COI gene sequences of 458 individuals. Analysis revealed three distinct evolutionary lineages, one of which, the so-called Lepidium host race, was only found on L. draba and appears to occur in a restricted geographic area, ranging between northern Spain and northern Italy. These results allow us to targeting sites for collection of the Lepidium host race and justify the prioritization of C. assimilis Lepidium host race as a candidate for the L. draba biological control.