Grasshopper (Orthoptera: Acridoidea) diversity in the Pampas region of Argentina: status as revealed by long-term sampling

This study, spanning 37 years, assessed the diversity of grasshopper communities across much of the Pampas region. Ninety-five sampling sites were established in Buenos Aires and La Pampa provinces. Five zones were defined: Northeast (NE), Northwest (NW), Southeast (SE), Southwest (SW), and West (W). Each site was categorized according to the dominant vegetation. A total of fifty grasshopper species from three families were collected. Acrididae was the most diverse (41 species). Rarefaction analysis indicated that the SE was the zone with the lowest species richness (Q0). The NE, SW, and W showed higher diversity (Q1), while NE was less diverse according to Q2. The PCA revealed varying abundances of species across zones, with some species more abundant in specific areas (e.g., Dichroplus maculipennis and Borellia bruneri in SE). The highest species count (50) was in grassland with grass dominance. The CA showed significant associations between grasshopper species and different grasslands (e.g., Covasacris pallidinota, Dichroplus maculipennis, and Parorphula graminae in Halophilous grassland). Beta diversity highlighted species turnover as key component in the SW, W, and NE, while in the SE it was nestedness. In the NW, turnover and species loss components affected beta diversity. Communities were dominated by a few species, with three or four species representing over 50% of the community. Some abundant species declined or disappeared over time, while others appeared later. These results provide the first quantitative analysis of the grasshopper fauna across much of one of South America’s most heavily modified ecosystems, the grasslands of the Argentine Pampas region.

For decades, the Pampas grasslands have been undergoing a significant transformation, with the replacement of grasslands by highly productive agroecosystems. Grasshoppers are among the most abundant insects in grasslands. Therefore, understanding whether this transition to intensive agroecosystems has affected the richness and diversity of grasshoppers is an important question. The results of this study highlight the importance of long-term ecological research (37 years), which has coincided with a period of significant agricultural intensification across the region. This intensification has resulted in a homogenization and fragmentation of natural grasslands, with consequent impacts on associated fauna. The observed trends of this study probably reflect the current state of the grasshopper fauna in the Pampas during the last decades, in an increasingly managed agroecosystem context.