Parasitoids of a Stem Weevil, Cylindrocopturus Adspersus (Coleoptera: Curculionidae), in Sunflower: Incidence and Parasitization Rates in the Northern Great Plains1

Abstract

Three species of Hymenoptera were reared from overwintering larvae of a sunflower stem weevil, Cylindrocopturus Adspersus (LeConte), collected in North Dakota, South Dakota, and Minnesota in 1979 and 1980. These included: Nealiolus curculionis (Fitch) (Braconidae); Tetrastichus ainsliei Gahan (Eulophidae); and Mesopolobus sp. (Pteromalidae). N. curculionis was the most prevalent, representing about 90% of the total number of parasitoids. All three species are endoparasitoids, overwintering within the host weevil larva. N. curculionis and Mesopolobus sp. are solitary parasitoids, and T. ainsliei is a gregarious parasitoid, yielding up to 13 adults per host. The percentage of sunflower fields with parasitized C. adspersus larvae averaged 76% in 1979 and 43% in 1980. Rates of parasitization of C. adspersus overwintering larvae by the three parasitoids were higher in 1979 than in 1980, with total means for the three states of 12 and 5%, respectively.