Responses of fly communities to restoration status, floral density, and grasshopper density in northeastern Montana

The seeding of crested wheatgrass (Agropyron cristatum) in the early 1900s to promote forage on rangelands has resulted in stable monocultures throughout northeastern Montana. Recently, the Bureau of Land Management has prioritized restoration projects to remove crested wheatgrass and restore native prairie plants that support sage-grouse. However, the effects of these actions on pollinators in this area, particularly flies, are poorly understood. We assessed fly communities and fly–plant interactions across three restorations of varying ages and treatments, an intact native prairie, and an unrestored site dominated by crested wheatgrass. The newest restoration site often exceeded the intact prairie in terms of fly visitation and the diversity of fly species and fly–plant interactions. However, the fly communities and fly-plant interactions at the restoration sites were compositionally distinct from those in the intact prairie, and some were more similar to the unrestored site. Fly visitation increased with floral density up to moderate levels. We observed more fly visits in areas where grasshopper density was greater than eight grasshoppers/square yard. Grasshopper densities were highest in the three restoration sites. Two of the most abundant fly visitors are larval predators of grasshopper eggs, and several of the fly families we observed have species in Montana that are parasitoids of grasshoppers. Our results suggest that gains in diversity alone do not indicate restoration success. While restoration goals to increase floral diversity likely support pollinators, larval host availability may also be influential for flies and should be considered for restorations in areas that are predominantly fly-pollinated.