Grasshopper populations of interior Alaska not limited by food

Grasshoppers can cause substantial losses to rangelands and crops, but chemical control of grasshopper pests is rarely justified because of the low value of forages, the extensive areas to be treated, and impacts to non-target organisms. More sustainable strategies to manage grasshopper populations require knowledge of the forces that regulate populations. In some systems, grasshoppers are food limited in most years, whereas in other systems top-down forces, e.g., predators, are implicated. This experiment was undertaken to determine whether grasshoppers are food-limited in Alaska. Cages were set up in a fallow field near Delta Junction, Alaska in 2007 and 2008. The experiment was a split-plot design with N fertilizer as among-plots effect and grasshopper density as the within-plots effect. Fertilizer was added to half the plots to increase primary production. Cages within each plot were stocked with 0, 5, 9, or 13 fourth-instar Melanoplus borealis (equivalent to 0, 20, 36, or 52 grasshoppers m^-2). Grasshoppers were counted weekly. Near the end of the growing season, surviving female grasshoppers were collected. Femur length was measured, and functional ovarioles were counted as a measure of potential fecundity. If the grasshoppers were food limited, I expected to see significant effects of either density or fertilizer on grasshopper survival, size, or fecundity. The fertilizer treatment greatly increased primary production in both years. Neither fertilizer treatment or grasshopper density had any effect on survival, size, or potential fecundity, leading me to conclude that food was not limiting at densities up to 52 grasshoppers m^-2