Interannual Variability in Acridian Community (Orthoptera: Caelifera: Acrididae) in Central-southern Uruguay

Abstract

Acridians (Orthoptera: Caelifera: Acrididae) are native insects that inhabit Uruguayan grasslands. Occasionally, abundance increases exponentially, as in the 1950' and in 2008/09, causing significant economic losses. This work aimed to describe the variation in the abundance and diversity of the communities that inhabit the grasslands of south-central region. Acridian populations were monitored during five seasons in Florida and Durazno sites. Cumulative and site-specific (S) richness, Shannon-Weiner (H ‘) diversity index, Pielou evenness (J’), qualitative similarity of Sorensen (Is), constance of presence (C), total abundance (A), and absolute and relative specific abundance were estimated. Based on these community descriptors and their temporal variations, we identified and characterized outbreak, transition and non-outbreak periods. In 2009/10 (outbreak) S, A, and Is, were highest, J ‘ and H’ were low, and Borellia bruneri (Rehn, 1906) was the most abundant species. The 2010/11 -2011/12 period (transition), was characterized by intermediate J’ and Is, low A and S, and B. bruneri remained predominant. During 2012/13 and 2013/14 (equilibrium), higher values of J ‘and H’, and low values of A, S and Is were recorded, and the relative abundance of B. bruneri decreased significantly. In this period Scotussa lemniscata (Stål, 1861) was the predominant species. These results indicate that in the grasslands of south-central region of Uruguay, the prevalence of B. bruneri, the decrease in J’ and increase in Is, would be indicators of a transition period to an outbreak.