Estimates of Nebraska rangeland grasshoppers: Sampling, distribution, and feeding preferences

Approximately 100 species of short-horn grasshoppers occur in Nebraska. Grasshoppers are of high economic and ecological importance because of their relatively large size, range of feeding habits, and reproductive potential. Grasshoppers are the most important insect pest in rangeland habitats in the United States with an estimated annual consumption of 21 to 23 percent of all available range forage in the western United States. My research examined three objectives aimed at improving knowledge of factors that affect sampling and subsequent estimates of rangeland grasshopper numbers: (1) The feeding preference of the grasshoppers Arphia xanthoptera (Burmeister) and Dichromorpha viridis (Scudder); (2) the impacts of time of day on the effectiveness of sweep sampling for rangeland grasshoppers; (3) rangeland grasshopper numbers and species composition in fields, fences, and roadside ditches across three regions of Nebraska.; Both Arphia xanthoptera (Burmeister) and Dichromorpha viridis (Scudder) were offered four plant species, consisting of two introduced cool season grasses; smooth brome (Bromus inermis Leyss) and Kentucky bluegrass (Poa pratensis L.), and two native warm season grasses; big blue stem (Adropogon gerardii Vitman), and sideoats grama (Bouteloua curtipendula Michx.). Results suggest that although these grasshoppers historically fed on native prairie grasses, the incursion of smooth brome in grasslands has altered their diet selection.; Preliminary observations while sampling rangeland grasshoppers at various times of day indicated differences in diversity and numbers captured. To confirm these observations, I used sweep net sampling at various times throughout the day and compared mean numbers among those times. Sweep sampling every hour from 06:00 to 12:00 revealed that grasshopper numbers to be significantly higher at 06:00 than both 07:00 and 08:00 (ANOVA, P<0.05). Laboratory behavioral studies conducted by placing adult Melanoplus femurrubrum (De Geer) in 208.2 liter (55 gallon) aquaria containing vegetation and exposing them to constant light, gradual light, or complete darkness revealed that light is not the main factor in observed sampling differences. My results indicate that standardized sampling of grasshoppers should be conducted between 10:00 and 16:00.; Economic thresholds throughout the U.S. are usually set at 9.6 adult grasshoppers per square meter (8 per square yard) despite wide variation in range conditions associated with geography and weather patterns. I compared the numbers of grasshoppers across approximately 400 km of northern Nebraska to document changes in species and densities. At each of 120 sites, the numbers of grasshoppers in the ditch, near the fence inside the field and approximate 30 meters from the fence in the field were recorded. Numbers and species composition of grasshoppers differed substantially across this region. Grasshopper numbers in the ditch and the field were similar with the lowest numbers observed near the fence. Based on the results, grasshopper sampling should be conducted more than 30 meters from the fence and thresholds in the ditch should be similar to those for other areas.; These results are significant in documenting native herbivore response to exotic vegetation, and in improving sampling design aimed at quantifying grasshopper numbers. Because grasshopper number estimates are used in decisions to treat large areas of rangeland, standardized sampling across both time of day and location in the field are critical considerations.