Grasshopper feeding mode differentially affects grass species cover in a northern mixed grassland

Little research has examined whether consistent levels of insect herbivory over multiple years affect plant composition in grasslands. We conducted a 7-yr manipulative experiment at a northern mixed-grass prairie site in eastern Montana, examining native grass cover in relation to herbivory by 2 grasshoppers with different feeding modes. The objective was to examine whether sustained levels of herbivory by 2 grasshopper species over 7 yr affected basal cover of the dominant grass species, western wheatgrass and blue grama. Blue grama cover was approximately 50% lower at the end of the experiment with a grass feeder Ageneotettix deorum (Scudder) relative to treatments without herbivory and with a mixed grass and forb feeder Melanoplus sanguinipes (Fabricius). The results appear to be driven by plant preference and feeding behavior, as A. deorum damaged blue grama blades more frequently. Although vertebrates typically have stronger impacts on rangeland plant composition, blue grama appears less resistant to herbivory by grass-feeding grasshoppers than cattle grazing in this mixed grass prairie. The results point to the need for further research on how grasshopper feeding mode affects rangeland function.