FEEDING-ACTIVITY OF MIDGE LARVAE (CHIRONOMUS-RIPARIUS MEIGEN) IN METAL-POLLUTED RIVER SEDIMENTS

A method was developed for monitoring the feeding activity of larvae o f the midge Chironomus riparius. The egestion rate (mg dry wt feces/mg dry wt larva/h) of the deposit-feeding larvae was measured and used a s an indication of the feeding activity. Both the egestion rate and su rvival of several metal-adapted and reference larvae were measured in five test sediments with various Cd and Zn concentrations. The referen ce larvae suffered increased mortality in two contaminated sediments b y comparison with field-exposed larvae. The feeding of all individuals decreased in the most polluted test sediment but also in another supp osedly clean reference sediment. No differences were found in egestion rates between the reference and field-exposed larvae, This observatio n, however, does not reliably answer the hypothesis whether the feedin g activity of the adapted and nonadapted midge larvae differs in metal -contaminated sediments because the data are based on total egestion d uring the short (96-h) experiment and the progress of feeding was not followed. (C) 1998 Academic Press.