Taxonomy and distribution of acridid grasshoppers in Nebraska and effects of temperature and immersion on rangeland pests

Prior to this study, Nebraska reported 100 species of short-horned grasshoppers (Orthoptera: Acrididae) from 2,185 county records. Between 2005 and 2007, 656 new county records and seven new state records were obtained. Knowledge of distribution, rarity, and potential pest status are complicated by taxonomic knowledge of some species in the state. As part of this work, I investigated three cases where taxonomic status is poorly known. Detailed studies of Chortophaga australior, a species of the southeastern United States, revealed that it does not appear to be a valid species but may represent a seasonal variant. Two grasshopper species which inhabit bare sandy soils, one on dry sand (Trimerotropis agrestis ) and one on moist sand (Trimerotropis maritima), appear to be hybridizing along the shores of Lake McConaughy, a phenomenon not previously observed between these two species. Although the recognized species in the Melanoplus packardii group which occur in Nebraska (Melanoplus foedus and Melanoplus packardii ) do not appear to maintain their integrity under the biological species concept, it appears that there may actually be three species in this group in the state under an ecological species concept. The results of my genetic studies on this group suggests that hybridization is frequent between all of these forms, but they are each morphologically distinct and do not hybridize when they co-occur at high densities. Various factors are known to influence grasshopper numbers and likelihood of reaching rangeland pest status. I tested survival of immersion, a mortality factor, previously hypothesized to be important in some instances. I also tested the effects of temperature on development for eight species of rangeland pests. This study found that direct mortality as a result of drowning is an uncommon event for most rangeland grasshoppers. Adults of species tested in this study survived on average 7.5 to 21 hours of immersion and hypoxia, while nymphs in the second and third instars survived an average of 3 to 13 hours. Sweep samples taken regularly over a prolonged period can be a useful tool in the prediction of degree-day requirements for rangeland grasshopper species and these data can be critical to current treatment methods. I calculated development thresholds for eight species of rangeland pests based on earliest adult occurrence across four regions of Nebraska. The results of this work will be improved management of potential rangeland pest species through knowledge of distribution, taxonomy of poorly-known species, and influences of weather events on development and survival