DIET AND GROWTH OF A LEAF-SHREDDING CADDISFLY IN SOUTHERN APPALACHIANSTREAMS OF CONTRASTING DISTURBANCE HISTORY

Diet and growth of leaf-shredding caddisfly larvae, Pycnopsyche spp., were examined in streams draining a reference catchment and a 16-year- old clear-cut (disturbed) catchment at Coweeta Hydrologic Laboratory i n southwestern North Carolina, USA. The objective was to explain why s hredder production is higher in the disturbed streams despite the larv ae having less food (i.e., leaves) available. We predicted larvae woul d grow faster on fast-decaying leaf material representative of the dis turbed streams. Larvae consumed mostly leaf detritus in three streams draining each catchment over three seasons (fall, winter, and spring), which showed larvae did not consume higher quality foods (e.g., algae and animal material) in disturbed streams. When fed 2-month-old condi tioned black birch (Betula lenta L.) (a fast-decaying leaf species) an d white oak (Quercus alba L.) (a slow-decaying leaf species) leaves in the laboratory, larvae grew significantly faster on the birch leaves. However, when larvae were fed the same leaf types after S-months cond itioning, larvae grew significantly faster on oak leaves. A field grow th experiment conducted for 42 d using mixed-species leaf diets repres entative of each catchment and initially conditioned for 2 months foun d that Pycnopsyche grew significantly better on the diet representativ e of the reference catchment. The 'reference diet' contained more oak leaves which apparently became a more acceptable food as the experimen t proceeded. High shredder production in the disturbed streams could n ot be explained by high Pycnopsyche growth rates on fast-decaying leav es. Instead, larvae grew better on leaves that were apparently conditi oned optimally regardless of conditioning rate.