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Abstract

Panicum virgatum L., commonly known as switchgrass, is a perennial bunch grass that is receiving attention as a potential candidate for biofuel production from its biomass (via conversion of cellulose to ethanol). Switchgrass is an extremely phenotypically diverse species that can be categorized into three main groups, called ecotypes, i.e., upland, lowland, and coastal ecotypes. The lowland ecotype has been reported to possess enhanced protection against itself from herbivores, specifically chewing insects such as fall armyworm (Spodoptera frugiperda J. E. Smith). The purpose of my study is to confirm in a large number of switchgrass lines prior suggestions on physical characteristics that may protect switchgrass against from herbivory, or that may serve as proxies for defense capacity. The characteristics investigated included average leaf area, leaf dry mass per area (LMA), leaf ash content, and latitude of origin. Multiple measures of herbivory were also assessed, including leaf area and leaf mass consumed by caterpillars, and change in caterpillar mass over the course of the feeding trials. Change in caterpillar mass turned out to be the best way to quantify herbivory under these lab conditions, because it accounted for leaf consumption by the caterpillar that did not lead to caterpillar weight gain. Leaf ash, total area per leaf and LMA were all negatively and significantly correlated with change in caterpillar mass and latitude of switchgrass ecotype origin was positively and significantly correlated with change in caterpillar mass. This information may be useful to inform the breeding of switchgrass varieties that are more resistant to herbivory and may thus have superior qualities as a biofuel crop.