Four Essays Concerning Grasshopper (Orthoptera: Acrididae) Outbreaks: 1) Impacts on Non-Target Arthropods following Large-Scale Grasshopper Suppression Programs; 2) Utilization of Remote Sensing to Detect Rangeland Grasshopper Infestations; 3) Long-Term T

摘要

These four studies were conducted to assess several questions enveloping rangeland grasshopper (Orthoptera: Acrididae) outbreaks (classified as densities >9.6 grasshoppers/m2) in eastern Wyoming. Specifically, these studies investigated 1) effects on non-target arthropods following diflubenzuron Reduced Agent and Area Treatments (RAATs) to suppress grasshopper outbreaks on native rangelands; 2) the use of remote sensing (and derived from it vegetative indices of NDVI or SAVI) to detect rangeland grasshopper outbreaks; 3) the hypothesis that a three-state Discrete Time Markov Chain (DTMC) using grasshopper species (instead of assemblages) will yield greater probabilities of predicting future grasshopper outbreaks than a two-state DTMC and to test ecological associations (elevation, slope, soil type and precipitation) of grasshopper outbreaks to compare results to previous studies using Geographic Information Systems (GIS); 4) whether particular grasshopper species associations are common during outbreaks that last >3 years. The results of this first investigation suggest nominal, if any, effects to non-target arthropods with the treatment methods described. The results of the second study report problematic techniques, ecological assumptions, and technological limitations in using remote sensing in this context of rangeland herbivory. Third, the Markov Chain analysis revealed that density-dependent factors may not play a role in population regulation for all grasshopper outbreaks and ecological analysis revealed that 70% of all grasshopper outbreaks recorded during the period of 1994-2011 occurred during above normal annual precipitation. Elevation, soil orders and vegetation type were also ecologically significant factors for grasshopper outbreaks in Wyoming. The fourth investigation revealed associations of certain grasshopper species with over 80% confidence.