LIFE-CYCLE AND PRODUCTION OF CHIRONOMIDAE (DIPTERA) FROM LAKE BANYOLES (NE SPAIN)

1. The life cycles and annual production of the eight most abundant sp ecies of chironomids (Procladius cf. choreus, Tanypus punctipennis, Ch ironomus bernensis, Chironomus gr. plumosus, Cladopelma virescens, Mic rochironomus tener, Tanytarsus gr. lestagei, and Cladotanytarsus atrid orsum) were studied from sublittoral and profundal samples taken month ly in Lake Banyoles during 1987 at five sampling stations (depths rang ing from 5 to 20 m). 2. The number of generations per year deduced fro m instar-frequency data varied from one to four, depending on the spec ies, 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. Prod uction estimates were calculated using the size-frequency (SF) method corrected for the number of generations (SFG), and the increment-summa tion 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 thre e species for which the use of the IS method was possible (C, virescen s, M, tener and C. atridorsum). Using these methods production was est imated to range from 23-70 mg AFDW (ash-free dry weight) m(-2) yr(-1) at 12 m to 74-275 mg AFDW m(-2) yr(-1) in the sublittoral zone of the lake (5-m depth). 5. Calculation of production for the other five spec ies using the size-frequency method with the number of generations (SF G) deduced from monthly instar-frequency data gave values ranging from 12 mg AFDW m(-2) yr(-1) (Chironomus bernensis at 20 m depth) to 3.75 g AFDW m(-2) yr(-1) (Procladius cf. choreus at 12 m). 6. Total chirono mid production (with the SFG method) varied from 0.8 to 5 g AFDW m(-2) yr(-1) in the profundal and sublittoral, respectively. At each sampli ng station two species groups accounted for most of the production: Pr ocladius cf. choreus and Chironomus spp. Annual production/biomass rat io (P/B) varied from very high values for Procladius (between 11 and 2 7, as four generations completed each year) to very low values for Chi ronomus gr. plumosus (2.20), which completed only one generation each year. The annual production of P. cf. choreus in Lake Banyoles is high er than any reported in the literature due to the completion of four g enerations and to the high densities of this species.