Variation in growth of the detritivore-shredder Sericostoma personatum (Trichoptera)

1. We investigated the growth of the detritivore-shredder Sericostoma perso natum by feeding groups of larvae on a fresh macrophyte, Potamogeton perfol iatus, conditioned sitka spruce needles, Picea sitchensis, conditioned alde r leaves, Alnus glutinosa, conditioned ash leaves, Fraxinus excelsior, and a fresh filamentous green alga, Microspora sp. A sixth treatment group of l arvae was fasted. 2. The nitrogen content of the food items ranged from 1.4% dry weight (DW) for Picea needles to 4.4% DW for Microspora filaments. Consumption of the v arious food items by Sericostoma differed significantly, being highest for Picea, and lowest for Potamogeton and Microspora. 3. The instantaneous growth rate ranged from -1.3% DW day(-1) in the fastin g group to 0.75% DW day(-1) in the Alnus group. The growth rate of larvae f ed on Alnus, Fraxinus and Microspora was similar, and significantly higher than that of the other three groups. An increase in the size of larval case s followed the same pattern as larval growth, although with less variation between food items. 4. Larvae fed on Microspora exhibited the greatest increase in fat content, while that of the larvae fed on Picea and those in the fasting group decre ased. The gross growth efficiency (G/I%) of Sericostoma (larva + case) rang ed from 2% when fed on Picea to 34% when fed on Microspora. Consumption was significantly correlated with the nutrient content of food items, whereas G/I% and growth rate were only weakly related to food quality. 5. The growth of Sericostoma varies with diet and the food items sustaining highest growth rate are not necessarily the 'typical' shredder food resour ces.