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Schlagwörter:
Sericostoma personatum; laboratory study; life cycle; light-dark dependence; daily consumption; microhabitat shift
Zusammenfassung:
The life cycle of Sericostoma personatum (Spence) was studied at 6°C, 10°C and 14°C and at each temperature at 8 and 14 hrs daylength. Embryogenesis was not temperature dependent in the 12°-18°C range. Only 7 of 38 (app. 18%) had a direct development, the rest remained in diapause with partly developed larvae. Hatching success of single egg masses was over 95%. At 6°C at both LDs, about 452 days are required for larval development. At 10°C 370 days (LD 8/16), or 320 days (LD 14/10) and at 14°C 319 days (LD 8/16) and 295 days (LD 14/10) were required. Duration of instars III and IV was longer at 6°C (both LDs), compared with all other groups. Vth instar larvae of the 14°C (LD 14/10) group grew fastest. Instar VI larvae of the 10°C short day group developed faster than all others. Instar VII larvae of both 14°C groups and of the 10°C long day group develop faster than the rest. Duration of pupal instar is only temperature dependent, regardless of light regime. The field life cycle of S. personatum may require 2-5 years. Larvae are night active. They feed on Coarse Particular Organic Material (CPOM) on the sediment surface at night. They release faeces (Fine Particular Organic Material, FPOM) into the sediment where they rest by day at a few cm depth. Their burrowing behavior thus contributes to the retention of FPOM in the stream channel. Daily food consumption at constant 10°C is significantly dependent on night length (r² = 0.979, p < 0.05). Two factors thus may limit food consumption: in winter, low temperatures, and in summer short nights. The species thus avoids competition by day-active shredders and predation by day-active predators. (DBO)
