A year-round study was conducted to examine feeding habits and food resources of the filter-feeding Trichoptera Arctopsyche grandis and Brachycentrus occidentalis along a regulated mountain stream gradient. There was a well defined longitudinal species replacement with A. grandis reaching maximum densities 2.3 kilometers below the impoundment, and concomitant with its decline downstream was an increase in B. occidentalis. At all sampling sites the < 75="" �m="" organic="" seston="" fraction="" usually="" consisted="" primarily="" of="" diatoms="" (="">70%, by areal estimate on microscope slides), whereas the 75?250 �m and > 250 �m seston fractions were predominantly composed of detritus (> 80 %). B. occidentalis larvae consumed primarily [...]
