Spatial and temporal distribution of black flies (Diptera: Simuliidae) in the Pampa biome streams, Brazil

Abstract

Several recent studies were conducted concerning species richness and spatial-temporal distribution of Simuliidae (Diptera: Culicomorpha), but there are still gaps in knowledge regarding these species, mainly when it comes to their local abundance and regional distribution patterns. The aim of this study was to investigate the distribution and diversity of Simuliidae in a watershed located in the Pampa biome of southern Brazil. Abiotic factors were evaluated during two seasons, spring and autumn, and at two spatial scales. These spatial scales consisted of three regions of the Piratinim river drainage basin (upper basin, middle, and lower courses) and three stretches of tributary streams (upstream, intermediate, and downstream). Immature stages, consisting of larvae and pupae, were sampled in six streams encompassing a total of 18 sampling points. The results indicated the occurrence of nine simuliid species along the studied area, with the three most abundant being Simulium pertinax, Simulium orbitale, and Simulium incrustatum. It was verified that the structure of the assemblage was mostly influenced by local factors, i.e., stream stretches, but also by those of a wider scale, i.e., watershed regions. Some species showed spatial distribution patterns; Simulium orbitale and S. jujuyense were associated with downstream areas, while S. pertinax was associated with upstream areas. Concerning regions, S. pertinax was less frequent in the lower region of the basin. Environmental variables such as temperature and stream width were also important. Our results show new and relevant information regarding the structure of simuliid assemblages in the Pampa biome.