Density-dependent effects of an early season insect herbivore on a later developing insect herbivore

Although most North American grasshopper species overwinter as eggs, some species hatch in late summer, overwinter as nymphs, and become adults in late spring. These species periodically reach outbreak densities, but it is unknown if they impact the population dynamics of later developing egg-overwintering grasshopper species. Two experiments were conducted in a northern mixed-grass prairie to examine the effects of herbivory by nymph-overwintering grasshoppers on survival of an egg-overwintering grasshopper, Ageneotettix deorum. When very high densities of nymph-overwintering grasshoppers reduced grass biomass by 80%, survival of A. deorum nymphs was significantly reduced. There was no effect of early season herbivory at a lower density of 16/m(2) on survival of A. deorum nymphs. The effects of early season herbivory appear consistent with exploitative competition. Although a strong reduction in peak grass biomass caused by early season herbivory negatively affected late season grass-feeding grasshopper densities, additional research is needed to examine the potential importance of early summer herbivory on population dynamics of later developing grasshoppers.