The Heteroptera composition in the middle course of the Jacuí River basin, RS, Brazil, and some abiotic factors that might affect their distribution and abundance were studied previously to the Dona Francisca dam construction. The insects were quantitatively sampled in six sites, in lentic environments, with sieves (January 2000). In lotic environments, the samplings of the benthic Heteroptera were carried out in thirteen sites with a Surber sampler (from May to October 2000). In each station, pH, dissolved oxygen, monthly precipitation, water and air temperatures, and depth were measured. In rivers and streams, the current velocity was also registered. Fifteen species were registered in the lentic environments, being Belostoma sp. and Notonecta sp. the dominant species (70%). Abundance, richness and diversity indexes were higher in sites with larger dimensions. In running waters, two species of Naucoridae were recorded, Ambrysus teutonius La Rivers, 1951 and Cryphocricus vianai De Carlo, 1951, being the former dominant (65%). The abundance was greater in sampling points with dense canopy and/or with litter, or with the macrophyte Podostemum sp. (Podostemaceae), and was smaller in semi-regulated sites. Possibly, the monthly abundance of the Naucoridae be influenced by abiotic factors, such as temperature and precipitation. The results of this study will subsidize future impact researches after Dona Francisca dam has been built.
Abiotic factors; aquatic insects; hydropower reservoir; macroinvertebrates; Rio Grande do Sul
