FEEDING ECOLOGY OF THE FRESH-WATER DETRITIVORE PTYCHOPTERA-PALUDOSA (DIPTERA, NEMATOCERA)

1. We examined selected aspects of the nutritional ecology of larval P tychoptera paludosa and their role in nutrient cycling in the Breitenb ach, a first-order stream in Hesse, Germany. 2. Food preference experi ments demonstrated significant preference for sediments with a high or ganic matter content and live bacteria. 3. pH was circumneutral in all sections of the gut. 4. Enzymatic activity (beta-glucosidase and amin o-peptidase) in different parts of the gut was measured using 4-methyl umbelliferyl-beta-D-glucopyranoside (MUF-Glc) and leucine-4-methylcoum arinyl-7-amide (Leu-MCA). beta-glucosidase activity was highest in the hindgut. 5. The mean larval gut passage time was between 7 and 8 h. 6 . The egestion rate of last instar larvae was about 0.35 mg dry weight (DW) faeces per larva h(-1) and about 1.25 mg ash-free dry weight (AF DW) faeces per mg larval AFDW day(-1). 7. Larval faeces contained at l east 4-18 times more organic matter than the average in the sediments in which they were feeding, that is, larvae fed selectively, extractin g organic matter from sediments. 8. P, paludosa larvae are important i n the dynamics of detritus in slow-flowing reaches of the Breitenbach. They gather organic material from the sediment to a depth of 3 cm, an d release it as faeces onto the sediment surface. A total of 770 g DW faeces m(-2) yr(-1), comprising about 16% organic matter, was produced by the Ptychoptera population.