Establishment ofRhinocyllus conicuson Milk Thistle in Southern California

Abstract

During 1971 and 1972, 4,400 adults ofRhinocyllus conicusFroelich 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 ofR. conicusat colonization sites are presented. Biotic mortality factors reported forR. conicusin southern California include predation of eggs by ladybird beetles (Hippodamiasp.) and of adults by snakeflies [Raphidia (Agulla) adnixaHagen] and spiders, destruction of weevils in flower-heads consumed by cattle and rodents, and larval and pupal parasitism by pyomotid mites.