Toward a General Model of Rangeland Grasshopper (Orthoptera: Acrididae) Phenology in the Steppe Region of Montana

A 4-yr study was conducted to examine the phenology of rangeland grasshoppers at 12 sites throughout Montana. A six-species complex of common and economically important rangeland grasshoppers was selected to facilitate comparisons between sites in this environmentally heterogeneous state. Results showed that a published phenology model (developed by Dennis, B., W. P. Kemp & R. C. Beckwith. 1986. A stochastic model of insect phenology: estimation and testing Environ. Entomol. 15: 540–546, and Dennis, B. & W. P. Kemp. 1988. Further statistical inference methods for a stochastic model of insect phenology. Environ. Entomol. 17: 887–893) provided good estimates of “general” grasshopper phenology for each site and year. Comparisons of developmental “signposts” (75% first instar, peak second to fifth instars, and 75% adults) for grasshoppers between sites and years indicated that they can be used by resource managers for estimating when development stages of rangeland grasshoppers are likely to occur. The developmental signposts were separated, on average, by 8–12 d. Implications of these results for rangeland insect pest management are discussed.