Rhinocyllus conicusFroeL., a thistle head-feeding weevil introduced from France, successfully controlledCarduus nutansL. (musk thistle) at a Virginia release site (Pulaski Co.) 6 yr after the initial release of 100 adults m 1969. Thistle density was reduced by 95%. This is the 1st documented success of musk thistle control by the introduction ofR. conicus. In 1974 and 1975, ca. 90% of the thistles were attacked by the weevil; over 10% of the terminal heads were aborted. The unaborted heads produced few viable seeds and only the later-blooming, smaller heads escaped severe infestation. Dispersal was only 1.6 km 3 yr after release, but after 6 yr both eggs and adults were detected 32 km from the original release site.