Grasshopper Stages of Development as Indicators of Nontarget Arthropod Activity: Implications for Grasshopper Management Programs on Mixed-Grass Rangeland

Abstract

A study was conducted to determine if grasshopper stages of development could be used as indicators of nontarget arthropod activity on mixed-grass rangeland. Densities of grasshopper species, instars, and adults were estimated at several plots in northwestern South Dakota at weekly intervals throughout the summers of 1986 and 1987. At each plot, activities of nontarget arthropods were determined from pitfall and malaise trap catches. Factor analysis was used to relate activities of nontarget arthropods (Carabidae, Tenebrionidae, Meloidae, Lycosidae, Gryllidae, Formicidae, Ichneumonidae, Sphecidae, Pompilidae, and Asilidae) with densities of grasshopper species and stages of development. Nymphs of most dominant grasshopper species were associated with Carabidae, Lycosidae, Sphecidae, and Asilidae, all groups known to prey on grasshoppers. Adults were associated only with Tenebrionidae. These results suggest that insecticides applied to rangeland when most grasshoppers are middle to late instars will have a maximum impact on nontarget arthropods.