Adults ofRhinocyllus conicusFroelich collected in southeastern Italy were released in See Canyon, California, for the biological control of Italian thistle,Carduus pycnocephalusL. Field data on the incidence and increase of this weevil at this colonization site are presented. Larvae destroyed ca. 90% of an avg 7.3 mature achenes in 300 infested flowerheads sampled in 1976. An avg of 1.8 (range 1–6) weevils was reared from each flowerhead. By 1977, 91% of 561 capitula examined in a 2 man-h search bore at least one and an avg of 3.4 (max 11) eggs; however, no population reduction of Italian thistle as yet was evident.Biotic mortality factors reported forR. conicusinclude a low incidence of larval parasitism by an unidentified species ofHabrocytus(Hym.: Pteromalidae) and occasional predation of adults by the crab spider,Xysticus californicusKeyserling (Araneida: Thomisidae).During 1976 and 1977, totals of 1800 and 6500 weevils from this established field colony were transferred to 4 and 13 new locations in southern California, respectively.