SPATIAL CHARACTERISTICS OF RANGELAND GRASSHOPPER (ORTHOPTERA, ACRIDIDAE) POPULATION-DYNAMICS IN WYOMING - IMPLICATIONS FOR PEST-MANAGEMENT

A raster-based geographic information system was used to analyze 31 yr of USDA grasshopper survey data from Wyoming to identify areas prone to grasshopper infestations of greater than or equal to 10 grasshopper s per square meter and to understand the spatiotemporal characteristic s of rangeland grasshopper population dynamics. A temporally consisten t, clumped spatial distribution was observed in the grasshopper infest ations. Frequently infested lands were usually surrounded by areas wit h less frequent infestations, which graded into areas of apparently su itable habitat with no recorded infestations. Sixty-two percent of Wyo ming has never had a recorded infestation, and only 6% of Wyoming has been infested greater than or equal to 6 times. There has been >1 mill ion ha infested in 12 yr, but <1% of Wyoming has been infested in grea ter than or equal to 8 yr. Five, major 2-yr outbreak expansion sequenc es showed localized spatiotemporal persistence; the sequences revealed that grasshopper densities can reach outbreak levels over wide areas in a single year. Five, major 2-yr outbreak collapse sequences exhibit ed limited spatiotemporal persistence, with collapsing outbreaks often leaving no remnant infestations. Grasshopper outbreaks appear to exhi bit characteristics of gradient dynamics at the scale of this study, a lthough eruptive dynamics can not be entirely discounted. Applications of these results to pest management survey and treatment decisions ar e considered.