none Flower heads and peduncles of musk thistle, Carduus thoermeri Weinmann, and flower heads of plumeless thistle, Carduus acanthoides L., infested with Rhinocyllus conicus Froelich were collected to study parasitism of the different developmental stages of the weevil in 1978 and 1979. No parasites of eggs or adults were found. Major larval-pupal parasites were Bracon mellitor (Say) (Braconidae), Nealiolus curculionis (previously known as Aliolus curculionis ) (Fitch) (Braconidae), Zatropis sp. (Pteromalidae), and Neocatolaccus sp. (Pteromalidae). B. mellitor, N. curculionis , and Zatropis sp. attacked R. conicus over a 4-week period; parasitism was greatest during the first 2 weeks of July. Rate of parasitization differed between locations on thistle plants, thistle species, sites with different periods of weevil establishment, years of collections, and sample date. Although high leels of parasitization sometimes occurred, the overall rate was low. Nutrition; Diet; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Host parasite relationships; Ecology; Habitat utilization; Land and freshwater zones; Nearctic region; North America; USA Rhinocyllus conicus (Curculionidae); Food plants; Carduus acanthoides (plumeless thistle) & C. thoermeri (musk thistle); Hymenopteran parasites relationship; Hymenopteran parasites; Prevalence & seasonal occurrence in larvae & pupae; Prevalence; Hymenoptera, season & food plant relationships; Habitat colonization; Population establishment, parasite prevalence relationship; Virginia; Prevalence of hymenopteran parasites, food plant & population age factors Hymenoptera; Coleopteran hosts; Rhinocyllus conicus; Prevalence in host larvae & pupae; Prevalence; Rhinocyllus conicus (Coleoptera), seasonality, factors; Virginia; Prevalence in coleopteran host larvae & pupae