The Relative Impact of Various Grasshopper Species on Stipa-Agropyron Mixed Prairie and Fescue Prairie in Southern Alberta

Abstract

Sweep-net samples of grasshoppers were taken annually in late August at Stavely (1970-78) on Festuca scabrella prairie and at Coalhurst (1971-79) on Stipa-Agropyron prairie. Mean catches of grasshoppers were higher (170 vs 112 per 50 sweeps) and more species were sampled (27 vs 13) at Coalhurst. Melanoplus dawsoni (Scudder) was the dominant grasshopper at Stavely while Encoptolophys sordidus costalis (Scudder) and Melanoplus infantilis (Scudder) were codominants at Coalhurst. Grasshoppers were also sampled at two other sites in 1971 and one in 1971 and 1972 on Stipa-Agropyron prairie. Mean catches per 50 sweeps were 122, 164, and 234, respectively, at these sites with 14, 12, and 11 species of grasshoppers sampled. The dominant species were Ageneotettix deorum (Scudder), M. infantilis, and M. dawsoni. Of the 35 species collected at the study sites, 21, those forming at least 1% of the grasshoppers collected at one or more sites, were evaluated for their potential impact on rangeland. Population counts and published data on phenology, damage to rangeland, and feeding preferences were considered. The per capita feeding rate of adults-assumed to be proportional to the 0.68 power of body weight-was also assessed. Using these criteria, all but two species-Melanoplus femurrubrum femurrubrum (DeGeer) and M. dawsoni-were considered potentially damaging. Adult weights varied such that an adult M. infantilis, the smallest species, would feed at 28% the rate of an adult Metator pardalinus (Saussure), the largest species. Published data on habitat preferences of the 21 species show that most of the damaging species prefer sparsely vegetated habitats and thus would be favored where range is overgrazed by cattle.