Grasshopper (Orthoptera: Acridoidea) and plant community relationships in the Argentine pampas

Aim The objectives of this study were to relate species density, richness and relative abundance of grasshoppers to habitat vegetation and to detect variations in these variables among native and exotic plant communities which reflected disturbance history. Location Twenty-seven sites were selected in 2000 representing a variety of native and exotic plant communities, with different degrees of disturbance history, in south-east Buenos Aires province, Argentina. Methods Grasshopper mean density, species relative abundance and species composition were estimated at each site via standard flushing and sweep net techniques. Plant associations at each site were estimated by evaluating the percentage canopy of ground cover of native perennial grasses, introduced perennial forbs, annual pastures, halophilous species, perennial pastures, native perennial forbs, introduced annual forbs and plant species richness. Based on vegetation variables, sites were classified into five disturbance categories: native grasslands, halophilous grasslands, pastures, moderately disturbed pastures and highly disturbed pastures. Results Grasshopper communities from sites dominated by introduced plant species (forbs, sown grasses and dicots), were characterized by relatively high densities and a high proportion of potential pest species. Native grassland sites showed lower grasshopper densities, while halophilous grassland had high densities, but with low proportion of potential pest species. Main conclusions Results from this study suggest that the most abundant and economic important species of the pampas, Dichroplus elongatus, was associated with sown pasture plants (grasses and dicots) and introduced forbs, and negatively correlated with natural communities (native vegetation and halophilous species). These relationships imply that appropriate management practices that leave more areas with natural vegetation and include perennial pastures and native species in the rotations could show beneficial in reducing the overall density and the proportion of the primary pest species in south-eastern Buenos Aires province.