Establishment ofRhinocyllus conicuson Milk Thistle in Southern California

Abstract
During 1971 and 1972, 4,400 adults of Rhinocyllus conicus Froelich were introduced into southern California from Italy for the biological control of milk thistle [Silybum marianum (L.) Gaertner]. These flowerhead-infesting weevils were colonized at nine, and successfully established at five, widely separated locations. Field data on the incidence and increase of R. conicus at colonization sites are presented. Biotic mortality factors reported for R. conicus in southern California include predation of eggs by ladybird beetles (Hippodamia sp.) and of adults by snakeflies [Raphidia (Agulla) adnixa Hagen] and spiders, destruction of weevils in flower-heads consumed by cattle and rodents, and larval and pupal parasitism by pyomotid mites.