ITALIAN THISTLE, Carduus pycnocephalus. L., and milk thistle, Silybum marianum (L.) Gaertn., alien weeds of Eurasian origin, have been studied since 1966 as targets of biological control in southern California. Found mainly in the coastal counties, these thistles are common weeds on grazing and pasture lands, open woodlands, fallow cropland, and wastelands such as roadsides, railroad rights-of-way, field margins, and ditch-banks. Field surveys from 1966 to 1971 established that both weeds were relatively free of deleterious insect injury. Most insects found associated with these weeds were sap- or foliage-feeding species which apparently had little influence on the vigor and reproductive capacity of these thistles in southern California.