Effects of prior herbivory by nymph-overwintering grasshoppers on survival of the egg-overwintering grasshopper species Ageneotettix deorum and peak biomass production

Background/Question/Methods

Plant mediated competition can occur between temporally separated herbivores, when herbivory by an early season species reduces the biomass or quality of host plants available for later developing species. Although most abundant grasshoppers in the northern Great Plains overwinter as eggs, a subset of species overwinter as nymphs and are adults by late spring. Nymph overwintering species can reach outbreak densities, but little is know about their effects on peak biomass production, the quality of vegetation available for later developing grasshopper species, and population dynamics of the later developing egg overwintering grasshopper species. A series of experiments were conducted at a northern mixed-grass prairie site in eastern Montana over three years to examine the effects of early season herbivory by nymph-overwintering grasshoppers on the survival of a common egg overwintering grasshopper species, Ageneotettix deorum.

Results/Conclusions

When initiated in cages at high densities, nymph overwintering grasshopper reduced peak biomass only in a year when early summer drought conditions reduced biomass production. However, even in the drought year there was no significant impact of the temporally separated early season herbivory by nymph overwintering grasshopper species on survival of Ageneotettix deorum nymphs. Although competition can occur between temporally separated herbivores, there was little indication of plant mediated competition resulting from early season herbivory on the later developing Ageneotettix deorum grasshoppers.