An undescribed microsporidium was isolated from a grasshopper species, Aulocara elliotti Thomas, in Platte County, Wyoming. A subsequent survey of grasshoppers revealed infections of the microsporidium in the other predominant grasshopper species, Psoloessa delicatula (Scudder). In a generation cycle, P. delicatula hatch in mid-summer, overwinter as late-instar nymphs, and become adults and oviposit in late spring, whereas A. elliotti diapause as eggs during winter, hatch in late spring, become adults and oviposit in early to mid-summer. The purpose of the present investigation is to report on the comparative incidence and transmission of the parasite in A. elliotti and P. delicatula.