The sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae), is a pest of cultivated sunflower (Helianthus annuus L) from the southern to the northern Great Plains. The incidence of weevil infestation in fields from the six different states sampled during 1996 and 1997 ranged from 33% (Minnesota) to 100% (Kansas, Colorado, Nebraska). Weevil populations in the fields sampled were statistically greater in the central Plains (Colorado, Kansas, Nebraska) with a mean of 12.3 and 19.5 larvae per stalk compared with the northern Plains (North and South Dakota, Minnesota) of 0.7 and 1.3 larvae per stalk in 1996 and 1997, respectively. Parasitization of weevils varied from field to field ranging from 1 to 100%, but was usually less than 20%. The nine species of larval parasitoids recovered were all Hymenoptera and included: Nealiolus curculionis (Fitch), N. collaris (Brues), Bracon sp. (Braconidae); Neocatolaccus tylodermae (Ashmead), Chlorocytus sp., Pteromalus sp. (Pteromalidae); Quadrastichus ainsliei Gahan (Eulophidae), Eurytoma tylodermatis Ashmead (Eurytomidae); and Eupelmus sp. (Eupelmidae). Nealiolus curculionis was the most prevalent parasitoid reared from C. adspersus, and it was recovered from all states sampled. Parasitoid species richness was greatest in the central Plains. The reduced number of parasitoid species found attacking C. adspersus in the northern Plains may be caused by low host population levels, slow migration by parasitoids into the region, or lack of adaptation to climatic conditions. Additional work to understand the population dynamics of the parasitoid complex associated with C. adspersus may result in improved biological control of the sunflower stem weevil in cultivated sunflower. none