Life cycle and secondary production of Agapetus quadratus (Trichoptera: Glossosomatidae) in a temporary stream of a Mediterranean island.

M. Alvarez and I. Pardo. Área de Ecología, Universidad de Vigo, 36200 Vigo, Spain.

The life cycle and production of a grazer, Agapetus quadratus (Mosely, 1930) were studied in the Gorg Blau torrent, a temporary stream on the Spanish Mediterranean island Majorca. Quantitative samples were taken every two-three weeks from November 2000 to July 2001 while the stream had water. The instars of field collected larvae and pupae, were determined by head width and pronotum length measurements. Frequency distribution and prepupal and pupal stages indicated a five instar cycle. Few prepupae were recorded at the sites, indicating that the duration of this stage is very short. Size-frequency histograms of field larva and pupae showed a trivoltine cycle, with an average cohort time of 4 months. Larval development was asynchronous, with continuous growth and overlapping generations. Recruitment (sum of first and second larval density) and maturation (sum of prepupal and pupal abundance) also supported a trivoltine life cycle. Three clear recruitment peaks were identified, late November, early March and late June, indicative of winter, spring and summer generations. Population densities and biomass derived from the field data were used to calculate secondary production (P) and turnover rate (P/B).