Seeking generalities in salt stress on herbivores: a multi-species approach

This study will examine how different insect herbivore feeding guilds react to salt-stressed coastal plants. Stress has been identified as one of the primary factors influencing the structure of food webs, but few conclusions about the effects of stress on community dynamics have emerged. By performing a multiple species examination, we tested whether or not herbivores from homologous feeding guilds respond similarly to stress conditions allowing for generalizations to be made about stress/herbivore interactions.

Plant responses were determined by assessing plant growth, leaf production, and flowering of six coastal plant species: Avicennia germinans, Baccharis halimifolia, Iva frutescens, Borrichia frutescens, Batis maritima, and Spartina alterniflora. Herbivore responses will be determined by visual herbivore counts, indirect visual evidence of insects (including galls, stem boring, and leaf mining), and sweep netting. The molecular component of this experiment will aid in quantifying plant stress, by measuring foliar nitrogen as well as the activity of certain stress enzymes; particularly catalase and superoxide dismutase.

Herbivore responses varied by guild. For example, chewers and miners were negatively affected, while mixed results were obtained for gallers and sap suckers. Stress enzymes were useful indicators of stress that affected herbivores even when the plant showed no visible signs of stress.

The ecological and molecular aspects of this study have allowed for a more thorough examination of the effects of salt stress in salt marsh food webs and have supplied data that could ultimately provide information for future management and sustainability of these complex systems.