Application of a Grassland Simulation Model to Grasshopper Pest Management on the North American Shortgrass Prairie1

Abstract An empirical grasshopper submodel was developed and used in conjunction with existing primary producer and abiotic submodels to assess the effects of grasshoppers on blue grama rangeland in Colorado. Density dependent mortality was incorporated, and this resulted in a temporal shift in occurrence of forage consumption by grasshoppers. Under high density conditions, proportionately more forage consumption occurred in early nymphal instars, than under low density conditions. Above-ground and below-ground plant standing crop values were estimated for various grasshopper densities, and for grasshoppers of three different size classes with three different consumption rates. Also, the influence of weather on standing crop was examined by providing recorded meteorological data from a site in Colorado for 1973–1975. Grasshopper consumption at low and moderate grasshopper densities resulted in a slight decrease in aboveground standing crop, and slight increase in below-ground standing crop. High levels of herbivory resulted in large decreases in both above-ground and below-ground standing crop. High levels of herbivory were more deleterious to below-ground standing crop during the two years with low precipitation than one year with higher precipitation.