Studies were conducted on rangeland in southwestern Idaho to evaluate the effect of moist, swalelike habitats on infectivity of an entomogenous fungus on two species of rangeland grasshoppers,Melanoplus bivittatus(Say) andMelanoplus sanguinipes(F.). Data clearly indicated that a significantly higher number ofM. bivittatuscollected from within the boundaries of four of five swale sites died from infection byEntomophaga calopteni(Bessey) Humber compared with infection levels among grasshoppers collected outside the swale margins. However, the incidence of infection ofM. bivitattusandM. sanguinipesdiffered significantly irrespective of location in or out of the swales. Disease incidence amongM. bivittatus, which was relatively abundant in moist habitats characterized by more succulent plant growth, was significantly higher. Results indicate that swales and other habitats that include a permanent or temporary free water component may support disease among some species of resident grasshoppers and thus serve as reservoirs of disease activity when weather conditions do not favor a widespread epizootic ofE. calopteni.