The temporal dynamics in density, life histories, and emergence patterns were described for the first time for five Plecoptera species in tributaries of the Futaleufú River in Patagonia, Argentina. Benthic samples and adult collections were made in five low order Nothofagus forested streams. Four species of Gripopterygidae; Aubertoperla illiesi, Notoperlopsis femina, Antarctoperla michaelseni and Senzilloides panguipulli had simple, highly synchronized univoltine life histories. The austroperlid Klapopteryx kuscheli takes more than two years to develop. Emergence periods of most of the species were concentrated in late spring and summer (October to February), which suggests seasonal and synchronized life histories. Most N. femina adults were collected in mid spring indicating this species emerged first, whereas S. panguipulli emerged last from January to April. Aubertoperla illiesi showed a slightly delayed emergence at the high elevation site (La Hoya Stream) when compared to a piedmont stream, suggesting that temperature was an important control. Although we were unable to describe the life history of Limnoperla jaffueli (Gripopterygidae) its adult emergence period was November to January. Life histories of Plecoptera species in the studied streams seem to have a high degree of seasonality at least at this latitude, and are possibly determined by predictable temperature patterns and discharge regimes. This first contribution on the life histories of Plecoptera species helps us to better understand the dynamics and functioning of pristine but fragile aquatic environments in Patagonia.

The habitat preferences, temporal dynamics in density and the life history of two species of mayflies, Metamonius anceps and Meridialaris chiloeensis, were investigated in a Patagonian mountain stream over a period of one year. Benthic samples were taken in a low order Nothofagus forested stream. M. anceps was univoltine with small nymphs predominating in winter and emergence occurring in summer. M. chiloeensis showed a bivoltine life cycle with a winter and summer generation, and emergence period in spring and summer. Both species were significantly more abundant in the low water period than in the high discharge season. Gravels supported significantly more individuals of M. chiloeensis than sand in pools and leaf packs. Temporal overlap of abundance between species was low. The existence of different life history strategies and the temporal shift of main generations and density peaks were critical to allow species coexistence.

Notoperla fasciata new species and Notoperla magnaspina new species are described, and a key given for the two species. The female and larva of Notoperlopsis femina are redescribed and the male is described for the first time. Notes on distribution, habitat and ecology are given.