Sunflower Stem Weevil and Its Larval Parasitoids in Native Sunflowers: Is Parasitoid Abundance and Diversity Greater in the U.S. Southwest?

Abstract

Classical biological control programs often target a pest's region of origin as a likely source for new biological control agents. Here, we use this approach to search for biological control agents of the sunflower stem weevil (Cylindrocopturus adspersus LeConte), an economically important pest of commercial sunflower. We conducted surveys of weevil natural enemy diversity and abundance across a transect running from the northern Great Plains to the southwestern U.S. (the presumed area of endemism of annual sunflower species in the genus Helianthus). Accordingly, natural enemy diversity and abundance were expected to be greater in the southwestern U.S. C. 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. Native H. annuus constituted the majority of the sunflower populations. Mean weevil densities were significantly higher in sunflower stalks that were larger in diameter. Mean weevil densities within sites did not differ across the range of longitudes and latitudes sampled. After accounting for the effects of stalk diameter and location, weevil densities did not differ among the four sunflower species nor did they differ as a function of elevation. C. adspersus in H. annuus and H. petiolaris were attacked by seven species of parasitoids. No parasitoids were found attacking C. adspersus 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 and increasing stem diameters. All parasitoid species have been previously reported attacking C. adspersus larvae in cultivated sunflower. Species richness was less diverse in these collections than from previous 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.

Crop Domestication and Its Impact on Naturally Selected Trophic Interactions

“…The effects of cultivation on the diversity and impact of natural enemies vary by system and herbivore species. Parasitoids associated with different herbivores may be more diverse and have a greater impact in natural sunflower ecosystems than in agroecosystems (30,36,141), may be similar in diversity and impact (27,111), or may have greater impact in agroecosystems (27). Predators were more abundant in natural ecosystems of wild rice than in irrigated rice agroecosystems, suggesting that the structural complexity and greater habitat persistence in wild rice enable a much more complex and diverse predator trophic level (33).…”

Getting western: biogeographical analysis of morphological variation, mitochondrial haplotypes and nuclear markers reveals cryptic species and hybrid zones in the Junonia butterflies of the American southwest and Mexico

“…Groups as diverse as birds (Bermingham et al ., ), mammals (Stein et al ., ), fish (Olden & Poff, ), plants [e.g. Helianthus (Ode et al ., )] and butterflies [e.g. Apodemia (Proshek et al ., ), Limenitis (Platt, ) and Speyeria (Williams, )] have greater endemic biodiversity in this region than in eastern North America.…”

Ovipositional Preference and Larval Performance of the Banded Sunflower Moth (Lepidoptera: Tortricidae) and Its Larval Parasitoids on Resistant and Susceptible Lines of Sunflower (Asterales: Asteraceae)

“…There are more than 600,000 ha of sunßower planted in the United States, yielding 900 million kg of seed worth US$600 million (National Agricultural Statistical Service [NASS 2012]). The genus Helianthus is indigenous to North America and has a species-rich insect complex associated with it, of which many species are either pests of cultivated sunßowers (Charlet et al 1997, Seiler andRieseberg 1997) or natural enemies of these pests (Ode et al 2011). The pests of sunßower can be classiÞed into three broad groups: head, foliage, or stem feeders of the plant.…”