The objective of the current study was to evaluate the distribution of the immature stages of Chirostilbia pertinax (Kollar, 1832) and associated bentic macroinvertebrates in relation to water velocity. This study was carried out on the upper course of Sinos river, in Rio Grande do Sul. Seasonal collections of larvae and pupae of black flies and associated benthic fauna were carried out at five places. In all sampling sites artificial substrates were installed, remaining submersed for 14 days in places of great water flow. Before removing the substrates the flow speeds on the collection sites were measured. To assess the distinct distribution patterns of the benthic fauna, the flow speed was divided in three classes: slow (0.20 - 0.63 m/s), medium (0.64 - 1.07 m/s) and fast (1.08 - 1.50 m/s). A total of 39,598 specimens were collected, from which 33,418 were black flies and 6,180 associated macroinvertebrates. From the total black flies, 5,704 were in the last larval instar and pupae from which 828 were C. pertinax. In the distribution of this species 30.8% occurred in slow flow, 24.9% in medium flow and 44.3% in fast flow. The abundance of C. pertinax is inversely related to the predatory macroinvertebrates (GLM, R² = 0.207; F 2.50 = 6.536; P = 0.003). These results demonstrate that the immature stages of C. pertinax have a tendency to occupy microhabitats with less predator occurrence.
Benthic macroinvertebrates; black flies; C. pertinax; water flow speed
