This study was carried out in two areas with different degrees of environmental degradation in the Caí river basin, in Rio Grande do Sul. One sampling area is less altered and the other is strongly impaired by organic pollutants from avian and swine production. The larvae and pupae of simulids were collected using artificial substrates that remain submersed in streams for 14 days. In all sampling sites water was collected simultaneously for physical-chemical and microbiological analysis. In the less disturbed area eleven species were collected with the following frequencies: Psaroniocompsa incrustata (42.95%), P. auripellita (17.66%), Chirostilbia pertinax (16.86%), Inaequalium subclavibranchium (8.43%), I. nogueirai (5.80%), P. anamariae (3.69%), I. clavibranchium (1.58%), C. riograndense (0.92%), Lutzsimulium hirticosta (0.92%), I. botulibranchium (0.79%), Thyrsopelma itaunense (0.40%). In the more disturbed area only six species were collected: C. pertinax (84.31%), C. riograndense (7.52%), T. itaunense (4.68%), P. incrustata (2.94%), I. subclavibranchium (0.33%), Ectemnaspis dinellii (0.22%). The concentrations of nitrate and nitrite had the greatest variations and allowed us to distinguish the sampling sites by to water quality. The nitrate concentration was significatively correlated with the occurrence of C. pertinax (r²= 0,54; P < 0,03) and T. itaunense (r²= 0,55; P < 0,03) while the nitrite concentration with C. riograndense (r²= 0,64; P < 0,02). These data can be useful for integrated black flies control programs, currently in use in at least 170 municipalities of Rio Grande do Sul.
Black flies; Nematocera; Neotropical; organic pollution; Simuliidae
