Freshwater Biology (1995) 33, 511-524 Life cycle and production of Chironomidae (Diptera) from Lake Banyoles (NE Spain) NARCfS PRAT AND MARIA RIHRADEVALL Department of Ecology, University of Barcelona, Diagonal 645, E-08028 Barcelona, Spain SUMMARY 1. The life cycles and annual production of the eight most abundant species of chironomids {Procladius cf. choreus, Tanypiis punctipennis, Chironomus bernensis, Chironomus gr. plumosus, Cladopelma virescens, Microchironomus tener, Tanytarsus gr. Jestagei, and Cladotanytarsus atridorsum) were studied from sublittoral and profundal samples taken monthly in Lake Banyoles during 1987 at five sampling stations (depths ranging from 5 to 20 m). 2. The number of generations per year deduced from instar-frequency data varied from one to four, depending on the species, lake basin and depth. Annual temperature range, dissolved oxygen in the stratified period and presence of sulphide are the key factors that may explain the differences in the number of generations. 3. Production estimates were calculated using the size-frequency (SF) method corrected for the number of generations (SFG), and the increment-summation method (IS) when cohorts could be clearly deduced. 4. Production calculated with the SFG method gave results which were comparable with those of the IS method using smoothed-survivorship curves in the three species for which the use of the IS method was possible (C. virescens, M. tener and C. atridorsum). Using these methods production was estimated to range from 23-70 mg AFDW (ash-free dry weight) m~^ yr"^ at 12 m to 74-275 mg AFDW m"^ yr"^ in the sublittoral zone of the lake (5-m depth). 5. Galculation of production for the other five species using the size-frequency method with the number of generations (SFG) deduced from monthly instar-frequency data gave values ranging from 12 mg AFDW m"^ yr~' {Chironomus bemensis at 20 m depth) to 3.75 g AFDW m"2 yr"' (Procladius cf. choreus at 12 m). 6. Total chironomid production (with the SFG method) varied from 0.8 to 5 g AFDW m"^ yr^^ in the profundal and sublittoral, respectively. At each sampling station two species groups accounted for most of the production: Procladius cf. choreus and Chironomus spp. Annual production/biomass ratio (P/B) varied from very high values for Procladius (between 11 and 27, as four generations completed each year) to very low values for Chironomus gr. plumosus (2.20), which coniipleted only one generation each year. The armual production of P. cf. choreus in Lake Banyoles is higher than any reported in the literature due to the completion of four generations and to the high densities of this species. Introduction As part of an extensive study of the ecology of the life cycles of several species of Ghironomidae and macrobenthic fauna, and especially of Ghironom^idae, provided estimates of their biomass and production, in Lake Banyoles (Rieradevall & Prat, 1989, 1991; Prat We studied eight species of chironomids, which consti- & Rieradevall, 1993; Rieradevall, 1991) we described tuted 98% of the larval density, from the sublittoral © 1995 Blackwell Science Ltd 511