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Effects of Nymph-Overwintering Grasshopper Density on Ageneotettix deorum Survival in a Northern Mixed Grassland

Branson David H.
Journal of orthoptera research 2011 v.20 no.2 pp. 137-139
Ageneotettix deorum, biomass, eggs, field experimentation, grasses, grasshoppers, grasslands, hatching, interspecific competition, nymphs, overwintering, pests, population density, spring, summer, North America
Although most pest grasshopper species in North America overwinter as eggs and hatch in late spring or early summer, some species hatch in late summer, overwinter as nymphs, and become adults in late spring. It is not well understood how nymph-overwintering species impact densities of later-developing pest grasshopper species. In an earlier study examining temporally separated competition, nymphal survival of an egg-overwintering species Ageneotettix deorum, was reduced when high densities of adult nymph-overwintering grasshoppers strongly reduced grass biomass. However, in nature, early instar A. deorum nymphs overlap in time with declining densities of nymph-overwintering grasshoppers, and thus may experience direct competition from them. A field experiment was conducted to examine competitive effects from nymph-overwintering grasshoppers on the survival of A. deorum when phenologies overlapped. Precipitation and grass production during the experiment were well above the long term average. Although the maximum density of nymph-overwintering and egg-overwintering grasshoppers was 100 per m², interspecific exploitative competition was weak. This study suggests that in years with above-average precipitation, competition between nymph-overwintering adult grasshoppers and later-developing nymphal grasshoppers is likely to be weak, even when densities are high.