Population dynamics, bioenergetics, and role of Lepidostoma quercina Ross (Trichoptera: Lepidostomatidae) in an Oregon woodland stream

The aim of this study was to gather quantitative field and laboratory data on theutilization of deciduous leaves as food by Lepidostoma quercina Ross (Trichoptera: Lepidostoma-tidae) and estimate the effect of this food processing on the stream ecosystem.
Samples were taken monthly in a riffle-pool section of Berry Creek, Benton County, Oregon.Maximum larval density was 382 per m2, instantaneous growth rate was 2.7% per day, instantaneousmortality rate was 1.4% per day, and production was 0.19 g m 2 yr-l. The life cycle of L. quercinaand its period of maximum larval growth corresponded closely with the period of maximum availabilityof its preferred food (alder leaves) in the stream.
Consumption and fecal production rates were measured gravimetrically. Rates (mg mg-'• day-1)increased with temperature, food quantity, and conditioning time of the leaves, and decreased withincreased size of the larvae.
Mean respiration rates of larvae were higher at 10°C than at 5°, but there was no significantdifference in mean rates at 10, 15, or 20°C. Respiration rate decreased with increased size of thelarvae. Size-specific respiration rates showed regulation of respiration with respect to temperaturefor small individuals (present in the field in September and October when temperatures are variable)and little or no regulation by large individuals (present in December and January).
Simulation modeling of larval growth based on laboratory data demonstrated that growth andproduction of L. quercina in the field may be limited by a lack of high-quality food (alder leaves) inlate summer and early fall. Consumption of leaves by the simulated population was estimated as 3.1
g. m-2. yr-1.
Lepidostoma quercina comprised only a small part of the secondary production in Berry Creek(0.19 g m-2- yr-', vs. 2.2 g • m-2 for simuliids) and processed only a small portion of the allochthonousinput to the stream. However, significant quantities of fecal material were produced and it wasestimated that these fine particles would be sufficient to support 'A to 1/2 of the production of simuliids,the dominant riffle species in Berry Creek.
Key words: bioenergetics; caddisflies; consumption; deciduous leaves; growth; Insecta; Lepi-dostoma; Oregon; population dynamics; respiration; stream.