Sandra Torrusio

Grasshopper (Orthoptera: Acrididae) community composition and temporal variation in the Pampas, Argentina

Abstract To evaluate temporal changes in grasshopper communities over a 5-y period (1997–2001), density and species relative abundance were estimated at 27 sites in Benito Juárez county, Southern Pampas, Argentina, established across vegetation associations with different disturbance histories. A total of 22 grasshopper species were collected, Melanoplinae being the most abundant and diverse subfamily, followed by Gomphocerinae, Acridinae, Copiocerinae and Leptysminae. Results allowed us to categorize years into nonoutbreak (1997, 1998, 1999), transitional (2000) and outbreak (2001) based on the spatiotemporal characteristics of grasshopper density trends. On average, grasshopper density was over 7 times greater in 2001 than in nonoutbreak years. During nonoutbreak years, grasshopper densities showed no significant variation across disturbance categories. During the outbreak year, densities were significantly higher in pastures and halophilous steppes, with highly disturbed pastures being the most affected sites of all. Species richness changed significantly in outbreak versus nonoutbreak years: nearly twice as many species were collected during the outbreak year. Although 22 species were collected, results showed that a small number influence overall abundance from nonoutbreak to outbreak conditions. Although Dichroplus elongatus, Covasacris albitarsis, and Scotussa lemniscata were the three topranked species throughoutthe studied period, D. elongatus contributed most to overall shifts in grasshopper density.

Field‐scale Variations in Plant and Grasshopper Communities: A GIS‐based Assessment

GIS technology allowed us to examine species-specific occurrence and abundance patterns of important grassland herbivore species through the use of appropriate statistical methods and the superior spatial representation commonly available in existing GIS packages. The study was conducted on a 254 ha grassland area located 10 km south of Three Forks, Gallatin County, Montana, in the Agropyron spicatum province of the western steppe region of the U.S.A. From an ecological perspective, grasshopper species distribution and abundance patterns observed on a local, non-uniform landscape (2.6 km 2) were consistent with results found in other studies at the valley (≈1,400 km 2) and state-level (≈237,000 km 2) scales. Our observations at the local scale further demonstrate the importance of vegetation type and specific local stand physiognomies in structuring grasshopper populations. The application of results from studies conducted at various scales to the development of decision support tools for resource managers is also discussed.

Influence of weather variables and plant communities on grasshopper density in the Southern Pampas, Argentina.

Abstract A study was conducted to evaluate the influence of weather (precipitation and temperature) and plant communities on grasshopper density over a 14-year period (1996–2009) in Benito Juárez County, Southern Pampas, Argentina. Total density strongly varied among plant communities. Highest values were registered in 2001 and 2003 in highly disturbed pastures and in 2002 and 2009 in halophilous grasslands. Native grasslands had the lowest density values. Seasonal precipitation and temperature had no significant effect on total grasshopper density. Dichroplus elongatus (Giglio-Tos) (Orthoptera: Acridoidea), Covasacris pallidinota (Bruner), Dichroplus pratensis Bruner, Scotussa lemniscata Stål, Borellia bruneri (Rehn) and Dichroplus maculipennis (Blanchard) comprised, on average, 64% of the grasshopper assemblages during low density years and 79% during high density years. Dichroplus elongatus, S. lemniscata and C. pallidinota were the most abundant species in 2001, 2002 and 2003, while D. elongatus, B. brunneri and C. pallidinota in 2009. Dichroplus elongatus and D. pratensis, mixed feeders species, were positively affected by summer rainfall. This suggests that the increase in summer precipitation had a positive effect on the quantity and quality forage production, affecting these grasshopper populations. Scotussa lemniscata and C. pallidinota were negatively affected by winter and fall temperature, possibly affecting the embryonic development before diapause and hatching. Dichroplus elongatus and D. pratensis were associated with highly disturbed pastures, S. lemniscata with pastures and B. bruneri and D. maculipennis with halophilous grasslands. Covasacris pallidinota was closely associated with halophilous grasslands and moderately disturbed pastures. Weather conditions changed over the years, with 2001, 2002 and 2003 having excessive rainfall while 2008 and 2009 were the driest years since the study started. We suggest that although seasonal precipitation and temperature had no significant effect on total grasshopper density, these weather variables and plant communities had differential influence on the dominant grasshopper species.