Rangeland Grasshopper Numbers and Species Composition in Nebraska: A Comparison of Region and Sampling Location

Abstract

Shorthorn grasshoppers (Orthoptera: Acrididae) are the most economically important pests of rangeland throughout much of North America. Their densities are estimated using a number of methods, including sweep sampling. Economic thresholds are usually set at 8 adult grasshoppers per square yard, despite differences in range conditions associated with geography and weather patterns. Several authors have concluded that grasshopper numbers are higher in ditch areas and the economic threshold in these habitats is often set substantially higher. This study compared grasshopper numbers and species composition at 120 rangeland sites across ∼ 400 km of northern Nebraska in 2007 and 2010. By taking sweep net samples in the ditch, parallel with the fence inside the pasture, and approximately 30 meters into the pasture, we found the numbers and composition of grasshoppers differed significantly across this area. Mean adult grasshopper capture was highest in the ditch samples (22.4 ± 1.9 grasshoppers captured per 20 net sweeps) compared to fence (10.3 ± 1.0) and field samples (15.9 ± 1.6). Mean adult capture increased from east (4.8 ± 0.4) to west (25.5 ± 2.1). The same trends were observed when nymphal numbers were included in analysis. Based on these results, rangeland grasshopper sampling should be conducted more than 30 meters from the fenceline, and thresholds in roadside ditches should be higher than for rangeland pastures.