Preference and performance of a generalist insect herbivore on Quercus agrifolia and Quercus engelmannii seedlings from a southern California oak woodland

摘要

Knowledge of the impact that insects have on oak seedlings planted in restoration programs is important for land managers and those interested in maintaining visible populations of a variety of oak species. Once established as seedlings, oaks face potential herbivory by mammals and phytophagous insects. To determine potential damage of a common generalist insect herbivore on oak seedlings, we conducted performance and preference tests using a grasshopper (Melanoplus sanguinipes) and two species of oaks (Quercus agrifolia and Quercus engelmannii) occurring in a southern California oak grassland. Q. agrifolia is abundant and often used in restoration plantings, while Q. engelmannii has the smallest range of all native oaks in California. To quantify herbivore performance, we measured leaf area of 30 Q. agrifolia and 30 Q. engelmannii seedlings, and caged them individually with a single grasshopper within acetate feeding arenas. Performance then was estimated by determining amount of leaf area eaten and frass produced. Grasshopper preference for either oak species was estimated in replicated choice experiments. M. sanguinipes consumed significantly more leaf area and produced significantly more frass when feeding only on Q. agrifolia than when feeding solely on Q. engelmannii. Additionally, grasshoppers feeding on Q. agrifolia gained significantly more biomass, whereas those feeding on Q. engelmannii actually lost biomass. Q. agrifolia provided a better diet than Q. engelmannii for this grasshopper species, a result that has the potential to affect the success of seedling planting programs in areas where both oaks and M. sanguinipes occur.