Seasonal Abundance and Impact of the Sunflower Stem Weevil Parasitoid, Nealiolus curculionis (Hymenoptera: Braconidae), in the Northern Great-Plains1

Nealiolus curculionis (Fitch) is a univoltine, solitary, endophagous larval parasitoid of the sunflower stem weevil, Cylindrocopturus adspersus (LeConte), in both cultivated and native sunflower. This parasitoid represented 96% of all parasitoids attacking the weevil from 1980 to 1991. Adult parasitoids were active in the field from late June to late August (1980-1985). Eggs were deposited in early instar weevils feeding within the sunflower stem. The immature parasitoids overwintered in diapausing weevil larvae in the sunflower stem. Parasitization of overwintering sunflower stem weevil larvae varied from 5 to 32% (1980 to 1991). Adult parasitoids emerged in early June through mid-July, which was earlier and more rapid than the emergence of their host. Postdiapause development of N. curculionis required 31 days after the parasitoid larvae exited the weevil larva for adult eclosion. Parasitoid males and females lived 9 days in the laboratory when supplied with honey as a food source. Results indicated that overall parasitization has increased from levels reported in the late 1970s and early 1980s. The parasitoid appears to be a consistent mortality factor in the population dynamics of the sunflower stem weevil in cultivated sunflower, though the adult populations are often low.