Assessing the biological control of yellow starthistle ( Centaurea solstitialis L): prospective analysis of the impact of the rosette weevil ( Ceratapion basicorne (Illiger))

1 Yellow starthistle (Centaurea solstitialisL) (YST) is an invasive weed native to theMediterranean region with a geographical centre of diversity in Turkey. It is widelyestablished in Chile, Australia, and western North America. It arrived in California asa contaminant in alfalfa seed in 1859 and, by 2002, had infested>7.7 million hectaresin the U.S.A. 2 Biological control of YST using capitula feeding weevils, picture wing flies and a foliarrust pathogen has been ongoing in the western U.S.A. for more than three decades withlimited success. Modelling and field research suggest natural enemies that kill wholeplants and/or reduce seed production of survivors are good candidates for successfulbiological control. A candidate species with some of these attributes is the rosetteweevilCeratapion basicorne(Illiger). 3 In the present study, a model of the rosette weevil is added to an extant system modelof YST and its capitula feeding natural enemies and, in a GIS context, is used toassess YST control in the Palearctic region and the weevil’s potential impact on YSTin western U.S.A 4 The results obtained suggest densities of mature YST plants in western U.S.A. wouldbe reduced by 70–80% in many areas.