Assessing the biological control of yellow starthistle ( C entaurea solstitialis L ): prospective analysis of the impact of the rosette weevil ( C eratapion basicorne ( I lliger))

Yellow starthistle ( C entaurea solstitialis L ) ( YST ) is an invasive weed native to the M editerranean region with a geographical centre of diversity in T urkey. It is widely established in C hile, A ustralia, and western N orth A merica. It arrived in C alifornia as a contaminant in alfalfa seed in 1859 and, by 2002, had infested >7.7 million hectares in the U.S.A . Biological control of YST using capitula feeding weevils, picture wing flies and a foliar rust pathogen has been ongoing in the western U.S.A. for more than three decades with limited success. Modelling and field research suggest natural enemies that kill whole plants and/or reduce seed production of survivors are good candidates for successful biological control. A candidate species with some of these attributes is the rosette weevil C eratapion basicorne ( I lliger). In the present study, a model of the rosette weevil is added to an extant system model of YST and its capitula feeding natural enemies and, in a GIS context, is used to assess YST control in the P alearctic region and the weevil's potential impact on YST in w estern U.S.A . The results obtained suggest densities of mature YST plants in western U.S.A. would be reduced by 70–80% in many areas.