Studies on the biology and host specificity ofEustenopus villosus(Boheman) were carried out in the field and laboratory in Greece and in the laboratory in Italy from 1981 to 1990. The weevil was first released in the United States for biological control of yellow starthistle,Centaurea solstitialisL. (Asteraceae: Cardueae), during 1990. In nature, overwintering adults appeared on bolting yellow starthistle plants by mid-May and were found until mid-July, south of Thessaloniki, Greece. Oviposition started at the beginning of June and the first pupae were found in early July. The first adults of the F1generation were found about mid-July in field-collected seedheads. Adults started to emerge gradually from seedheads from mid-July to the end of August and hibernated in cracks in the soil and among debris on the soil surface.E. villosusis univoltine and had three instars under laboratory conditions. Mating and feeding behavior, fecundity, and mortality are described. Adults fed on meristematic tissue and caused severe damage to the plants, and larvae fed in developing seedheads and reduced seed production up to 100% in infested seedheads. Because there is up to 97% mortality of the immature stages, the weevil does not build up dense populations in its native area.