Rangeland Grasshoppers (Orthoptera: Acrididae): Modeling Phenology of Natural Populations of Six Species

Abstract

Data were collected near Roundup, Mont., on phenology of six species of rangeland grasshoppers for 2 years. Logistic probability distribution was used to describe timing of developmental stages (instar 1 through adult) for each generation as a function of accumulated degree-days. Model results showed that there were significant differences in seasonal phenology between the generations for populations of each of the six species examined. However, average number of accumulated degree-days (17.8°C base) before peak instar 3 each year for the six species varied only slightly between seasons. Interspecific comparisons indicated that of the six species, Melanoplus infantilis Scudder developed fastest. Model design, assumptions, and applications as a descriptive tool are discussed, as are potential uses of the model to pest managers.