Impact of predation by the robber fly Proctacanthus milbertii (Diptera: Asilidae) on grasshopper (Orthoptera: Acrididae) populations

The impact of predation by the robber fly Proctacanthus milbertii Macquart on populations of adult grasshoppers from grasslands of the Nebraska sandhills was estimated. Densities of P. milbertii were estimated at 437 individuals per hectare (2 se=122). Overall densities of 23 species of grasshoppers were estimated to be 64,000 individuals per hectare with the most abundant species (Ageneotettix deorum) having a population size of approximately 15,000 individuals per hectare. Based on three estimates of predation level (ranging from 0.5 to 2 prey per day per robber fly), P. milbertii may take from 0.5% to 2% of the adult grasshoppers per day. Species of grasshoppers were taken by P. milbertii in about the same proportion in which they occurred at the study site and no size-selective component of predation was detectable.