Dissertation Research: Influence of Feeding Style on Herbivore Impacts: A Comparison of Leaf and Sap Feeding Insects

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Although insect herbivores are a diverse group and attack plants in a variety of ways, few studies have compared the impacts of different types of insect feeding on a host species. This research will examine how an insect's feeding style affects its impact by comparing three insects that feed on goldenrod (Solidago altissima): a leaf chewing beetle (Trirhabda sp.), a phloem feeding aphid (Uroleucon caligatum), and a xylem tapping spittlebug (Philaenus spumarius). Plants will be grown in pots and insects will be placed on them at densities that span the range of actual insect densities observed in our long-term censuses of goldenrod insects. Impacts on both reproductive and vegetative growth will be investigated. Effects on fitness will be evaluated by measuring fecundity, mean seed weights, rhizome weights, and nitrogen content of seeds and rhizomes. Plant allocation to buds, leaves, stems, and roots will be determined, as will leaf area and leaf nitrogen levels. A second objective is to see how herbivore impacts vary with the nutrient status of the host plant. Plants will be grown at two levels of soil fertility to see how impacts on plant fitness are effected. It is not currently possible to predict which types of insect feeding will be most damaging to plants, and this study will help to fill that gap.