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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Plant Science

First Advisor

Paul J. Johnson


Switchgrass (Panicum virgatum L.) is considered a potential model for an alternative fuel source in North America. Recently, two insect pests of switchgrass have been identified. The switchgrass moth [Blastobasis repartella (Dietz): Lepidoptera: Coleophoridae] feeds in the basal internodes and in rhizomes, causing premature tiller and rhizome loss. The switchgrass midge (Chilophaga virgati Gagné: Diptera: Cecidomyiidae) feeds above the last internode of the tiller, causing seed yield and biomass loss. There were two objectives for this study: (1) to determine genetic and temporal variation among cultivars for frequency of tiller infestation by switchgrass moth larvae in mature stands in the northern Great Plains and if variation in biomass production was associated with variation in frequency of infestation, in two trials (plots/established in 2004 and 2008) and (2) to increase knowledge of the biology of the gall midge by describing its life stages, phenology, and parasitoids in the Northern Great Plains. Data collection and observations were made during 2011 and 2012. In plots from 2008, differences were found among cultivars for tiller density, biomass yield, and numbers of leaves per healthy and infested tillers. Mean frequency of infestation was different between 2011 (6.7%) and 2012 (9.6%). Regression of biomass on frequency of infestation showed negative linear relationships for `Carthage’ and `Kentucky 1625’. However, in plots from 2008, differences were found among cultivars for tiller density and numbers of leaves per healthy. Mean frequency of infestation ranged from 2.6% for `Cave-In-Rock’ to 4.5% for `Pathfinder’ and was different between 2011 (2.7%) and 2012 (4.4%). In general, infested tillers had 1 less collared leaf than healthy tillers. Weights of healthy tiller were more >3x those of infested tillers. Switchgrass gall midge adult is active from early June to mid/late July. It overwinters as a late instar larva. The number of larvae ranged from 6 to 85. `Cave-In-Rock’ was more infested (>2x) than `Dacotah’ m-2. New parasitoids were reared from switchgrass gall midge larva: Quadrastichus sp. (Hymenoptera: Eulophilidae) and Platygaster chilophagae Buhl (Hymenoptera: Platygastridae). Results of this study are valuable to scientists for optimizing seed and biomass yields of switchgrass.

Library of Congress Subject Headings

Switchgrass -- Diseases and pests -- Great Plains
Arthropod pests -- Great Plains


Includes bibliographical references.



Number of Pages



South Dakota State University


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