Submitted to: Entomological Society of America Annual Meeting North Central Branch
Publication Type: Abstract Only
Publication Acceptance Date: March 28, 1999
Publication Date: N/A
Technical Abstract: The sunflower stem weevil is a pest of cultivated sunflower throughout the central and northern Great Plains. Larvae construct overwintering chambers in the sunflower stalk and when weevil populations equal 30-40 per stalk, plants may lodge prior to harvest resulting in loss of the entire head. Surveys were conducted in 1996 and 1997 to determine stem weevil infestation levels and parasitization throughout the central and northern sunflower production regions. Another goal was to determine if there were changes or shifts in the parasitoid species recovered from the different locations. Sunflower stalks were collected from 97 commercial sunflower fields in Colorado, Kansas, Nebraska, Minnesota, South Dakota, and North Dakota, during the two year study. The stalks were subjected to cold treatment to break diapause, dissected, and the weevils extracted and reared for emergence of adults or parasitoids. The incidence of weevil infestation in fields from the different states ranged from 33% (Minnesota) to 100% (Kansas, Colorado, Nebraska). Weevil populations per stalk were also greatest in the central Plains (1-68) compared with the northern Plains (0-12). Parasitization of weevils varied from field to field ranging from 1 to 100%, but was usually less than 20%. The parasitoids recovered were all Hymenoptera. Nealiolus curculionis was most common and was recovered from all states. Parasitoid species richness was greatest in the central Plains' production region.