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Free keywords:
Isoptena; Plecoptera; Insecta; Europa; running water; sandbed; morphology; ecology; biology; egg development; life cycle; nutrition
Abstract:
Larvae of the European stonefly Isoptena serricornis (Pictet) live buried in shifting sand and prefer erosional over depositional habitats. Specimens from Germany, Sachsen-Anhalt, were studied in laboratory streams. The species is univoltine. Eggs develop directly between ca 12 and 21°C; at 7°C development is delayed, at lower temperature it fails. Setal screens on the head are used to shovel sand away; screens also protect articulations. First instar larvae live on yolk reserves. Later instar larvae swallow entire Oligochaeta, larval Chironomidae and sediment-dwelling Leuctra nigra (Olivier) (Plecoptera, Leuctridae) were not eaten. Mode of hunting is unknown. Feeding larvae contain much sand in the fore-gut which may extend far into the abdomen. Individual sand grains may be half as wide as the head. Amount of sand in the gut decreases with body size; between 40 and 75 % of larval dry weight are ash. In view of gut structure, sand cannot be used to grind food; probably, sand is ballast permitting the larvae to live in erosional habitats. In the laboratory, adults emerged at dusk as soon as larvae were full grown. Adults ate little, and indiscriminately. Signalling was not observed, mating occured upon encounter, oviposition followed at the age of 8-10 days. Potential fecundity was 75 eggs or less. Eggs are large, compared with other Perloidea.
