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Seed weevils and their associated parasitoids were collected from sunflower heads of eight Helianthus spp. in seven states of the northern Great Plains. Native Helianthus annuus L. constituted the majority of the populations. Weevil larvae collected included both the red and gray sunflower seed weevils, Smicronyx fulvus LeConte and S. sordidus LeConte, respectively. The gray sunflower seed weevils represented 92.4% of the adults collected. Weevil larvae occurred in most samples of sunflower heads; usually more than one-half of the samples contained one or both weevil species. Density of weevil larvae was low, usually less than one larva per sunflower head. Each native species of sunflower, except H. annuus, had a lower incidence of the red sunflower seed weevil than gray sunflower seed weevil. Populations of some sunflower species may possess genes offering resistance to the red sunflower seed weevil and should be evaluated further for resistance to the species. We identified five species of endoparasitic Hymenoptera from the two weevil species, Eutrichosoma mirabile Ashmead (Pteromalidae) and four species of Braconidae; Urosigalphus femoratus Crawford, Nealiolus rufus (Riley), N. curculionis (Fitch), and Triaspis aequoris Martin. U. femoratus was the most prevalent parasitoid species, representing ≈45% of the adults reared from the weevil larvae. These parasitoid species, except N. curculionis, represent new host records from the red and gray sunflower seed weevils. Parasitization rates averaged 0-18.0%. Weevil larvae in seeds of native sunflowers were parasitized more heavily than others have reported for larvae from seeds of cultivated sunflower.
Charlet et al. (Tue,) studied this question.