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Abstract:
1. Egg masses, oviposition site preferences, and abiotic and biotic factors causing mortality during embryonic, larval and adult life stages of Apatania fimbriata were studied. Laboratory investigations provided information on the temperature dependence of embryonic development, measured as an increase in egg volume.
2. A. fimbriata laid hemispherical egg masses, consisting of a transparent matrix containing a mean of 208 eggs. Egg masses were laid on stones situated just above the water surface in dark cavities in the stream bank.
3. Two hundred egg masses were mapped and individually monitored during embryonic development. There was no significant correlation between mortality during embryonic development and any of the abiotic parameters measured. First-instar larvae of Osmylus fulvicephalus consumed developing eggs, and chironomids preyed on newly hatched larvae.
4. A mean of seventy-two females emerged per metre of stream. Mortality during the 1993/94 life cycle was measured as a percentage of the potential number of eggs laid. Female mortality between emergence and oviposition was ≈80%. Eight per cent of individuals were lost during embryonic development. Larval mortality to emergence in 1994 was 11.3%. This indicates that the terrestrial life stage is probably decisive in the regulation of A. fimbriata populations.
5. Duration of embryogenesis at constant temperatures (4-20 °C) in the laboratory was described best by a negative exponential function. This species is cold stenothermal and there was no hatching success at 20 °C.
6. Egg volumes during embryonic development increased sigmoidally over time.
