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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower and Plant Biology Research » Research » Publications at this Location » Publication #252103
Title: Sunflower stem weevil and its larval parasitoids in native sunflowers: Is parasitoid abundance and diversity greater in the US Southwest?

Author
item ODE, PAUL - Colorado State University
item Charlet, Laurence
item Seiler, Gerald

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2010
Publication Date: 6/1/2011
Citation: Ode, P.J., Charlet, L.D., Seiler, G.J. 2011. Sunflower stem weevil and its larval parasitoids in native sunflowers: Is parasitoid abundance and diversity greater in the U.S. Southwest?. Environmental Entomology. 40(1):15-22.

Interpretive Summary: Sunflower, which is a member of the genus Helianthus, is native to North America and insects associated with the wild species over time have moved into the cultivated crop and a number have caused economic losses for producers. The sunflower stem weevil is a pest of cultivated sunflower from the southern to the northern Plains. A study was conducted to compare numbers of weevils in wild sunflowers to locate plants with resistance genes and also to search for new natural enemies that could potentially provide control of this pest in commercial sunflower. Sunflower stem weevils and their larval parasites were collected from stems of four native sunflower species from 147 sites across eight states in 2003 and 2005. Native Helianthus annuus constituted the majority of the sunflower populations collected. Sunflower stem weevil larvae were found at nearly all locations and in all species except one. Mean weevil densities were significantly higher in sunflower stalks that were larger in diameter. Mean weevil densities were higher at sites located at middle longitudes and latitudes. After accounting for the effects of stalk diameter and location (both latitude and longitude), weevil densities did not differ among the four sunflower species nor did they differ as a function of elevation. Sunflower stem weevils in H. annuus and H. petiolaris were attacked by six species of parasites. No parasites were found in H. nuttallii or H. pauciflorus stalks. Stem weevils were twice as likely to be attacked by a parasite when feeding on H. petiolaris as H. annuus. Furthermore, the likelihood that stem weevils would be parasitized decreased with increasing elevation. All parasitoid species recovered had been previously reported attacking weevil larvae in cultivated sunflower. Our findings suggest that the species of larval parasites attacking sunflower stem weevil in native sunflowers have successfully made the transition to cultivated sunflower to parasitize this pest species.

Technical Abstract: Sunflower stem weevils (Cylindrocopturus adspersus) and their larval parasitoids were collected from stems of four native sunflower species (Helianthus annuus, H. nuttallii, H. pauciflorus, and H. petiolaris) from 147 sites across eight states in 2003 and 2005. Native H. annuus constituted the majority of the sunflower populations. Sunflower stem weevil larvae were found at nearly all locations and in all species except H. nuttallii for which only one population was sampled. Mean weevil densities were significantly higher in sunflower stalks that were larger in diameter. Mean weevil densities were higher at sites located at middle longitudes and latitudes. After accounting for the effects of stalk diameter and location (both latitude and longitude), weevil densities did not differ among the four sunflower species nor did they differ as a function of elevation. Sunflower stem weevils in H. annuus and H. petiolaris were attacked by six species of parasitoids. No parasitoids were found in H. nuttallii or H. pauciflorus stalks. C. adspersus were twice as likely to be attacked by a parasitoid when feeding on H. petiolaris than H. annuus. Furthermore, the likelihood that C. adspersus would be parasitized decreased with increasing elevation. All parasitoid species have been previously reported attacking C. adspersus larvae in cultivated sunflower. Species richness was less diverse in these collections than from earlier studies of cultivated sunflower. Our findings suggest that the species of larval parasitoids attacking C. adspersus in native sunflowers have successfully made the transition to cultivated sunflower to parasitize this pest species.