Investigations on Rangeland Grasshoppers: Ecoregion Level Distribution, Identification, Feeding Performance, and Vegetation Clipping

Short-horned grasshoppers (Orthoptera: Acrididae) were studied in the field as well as in laboratory for their distribution, identification, preferred food plants and feeding damage. These grasshoppers are important potential pests of rangelands where they compete for forage with cattle. Examination of the 20 most common grasshoppers by levels 3 and 4 of Nebraska ecoregions revealed specific habitat use and may be helpful in predicting hotspots. The relative abundance of all species analyzed showed at least some significant differences at ecoregion level 4 and two species showed single ecoregion that differed from all others at level 3. Grasshoppers belonging to subfamilies Melanoplinae, Gomphocerinae and Oedipodinae differ in biology and ecology, and were tested in a greenhouse experiment for feeding preference on switchgrass cultivars (Shawnee, Kanlow) and big bluestem. The data indicated a strong preference of Melanoplus differentialis for switchgrass (P ≤0.001). Melanoplus femurrubrum and Arphia xanthoptera also preferred the Shawnee cultivar. Further, the relative water content of the plants influenced consumption by M. differentialis which ate more healthy leaves than wilted leaves. The differences among grasshopper species suggested that Melanoplinae grasshoppers could become destructive pests of switchgrass fields. In addition to consumption, grasshoppers also cause feeding damage through vegetation clipping. Two grasshopper species were tested to quantify the amount of clippings at high, moderate and low moisture levels for little bluestem, Schizachyrium scoparium and buffalograss, Bouteloua dactyloides. All tested grasshopper species generated clippings. Relative water content of the grass affected the amount of clipping and differed by grasshopper and plant species. The results indicated that water content of the plant and species of grasshopper are important factors in damage. This study will aid in defining economic injury levels for rangeland grasshopper species. Two unidentified forms Melanoplus bowditchi frigidus and Melanoplus bowditchi tridentatus along with described subspecies of M. bowditchi were compared for morphological and genetic variations. No consistent differences among the aedeagal parameres or basal rings of the four forms were found. Amplified Fragment Length Polymorphism markers (AFLP) were used to test the genetic variation among the forms. Although the forms show behavioral and minor morphological differences, the genetic data showed all forms interbreed. The results of this study indicate that host plants can influence phenotype and suggest the need for further genetic analysis of subspecies recognized based on morphology. Advisors: W. Wyatt Hoback, John E. Foste