GROWTH AND ENERGETICS OF A TRICHOPTERAN LARVA FEEDING ON FRESH SUBMERGED AND TERRESTRIAL PLANTS

We studied the growth and assimilation of larvae of Anabolia nervosa, a lotic trichopteran shredder, on diets of fresh tissue of the submerg ed macrophyte Potamogeton perfoliatus and fresh leaves of the trees Al nus glutinosa and Fagus sylvatica. Fifth-in-star larvae were fed these three diets for 23 days (20 May-12 June) in the laboratory. Instantan eous growth rate and gross growth efficiency were almost the same for larvae fed Potamogeton and Alnus, but lower for larvae fed Fagus. The larvae consumed 3 times more fresh Potamogeton than Alnus leaves, but the same amounts in terms of dry mass. The consumption of fresh Fagus was initially twice that of the two other food items but dropped rapid ly during the experiment, following the marked seasonal decline of lea f nitrogen content. Allocation patterns of fat and protein differed am ong food sources. Larvae grown on Alnus accumulated more fat than larv ae grown on Potamogeton, while the reverse was true for protein accumu lation. The assimilation efficiency based on carbon units was the same (44%) for all three food items and was among the highest reported for shredding caddis larvae. The study demonstrates that fresh tissue of Potamogeton perfoliatus provides a valuable food source to the faculta tive shredder herbivore Anabolia nervosa.