title: Changes in western wheatgrass foliage quality following defoliation: consequences for a graminivorous grasshopper.
abstract: We determined the effects of defoliation by a graminivorous grasshopper on the foliage quality of the C3 plant, western wheatgrass (Pascopyrum smithii [Rydb] A. Love). Additionally, we determined the effects of this defoliation upon the subsequent feeding of the graminivorous grasshopper Phoetaliotes nebrascensis Thomas (Orthoptera: Acrididae). In field and greenhouse studies, graminivorous grasshopper herbivory altered the quality of remaining western wheatgrass foliage. In the greenhouse, severe (50% foliage removal) grasshopper grazing (638 grasshoppers/m2for 72h) resulted in decreased foliar nitrogen (-12%), carbohydrate (-11%) and water (-2.5%) concentrations, and increased phenolic concentrations (+43%). These changes were associated with decreased adult female grasshopper mass gain, consumption rate, approximate digestibility, and food conversion efficiencies. In the field, moderate (14% foliage removal) grasshopper grazing (20 grasshoppers/m2for 20 days) led to a 10% reduction in foliar nitrogen concentrations. Foliage quality changes in the field were not associated with any reductions in grasshopper mass gain, consumption rates, food digestibility, or conversion efficiencies. The results presented here are consistent with the hypothesis that defoliation leads to a reallocation of carbon and nitrogen compounds within the plant such that foliage quality for P. nebrascensis is reduced.
authors.affiliation: Department of Entomology, University of California, 92521, Riverside, CA, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Redak
authors.affiliation: Department of Entomology and Nematology, University of Florida, 32611, Gathesville, FL, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Capinera
keywords: Grasshoppers; Herbivory Plant quality; Orthoptera; Western wheatgrass