Production of Brachycentrus spinae Ross (Trichoptera: Brachycentridae) and its Role in Seston Dynamics of a Southern Appalachian Stream (USA)

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Abstract
Brachycentrus spinae Ross had a univoltine life cycle similar to other Brachycentrus spp. Larvae hatched in May, developed through five instars, and pupated in March. Larval production, excluding silk secretions, was 260.686 mg AFDW m −2 yr −1 , and mean annual standing crop was 40.396 mg AFDW m −2 . Annual and cohort turnover ratios (Production/Biomass) were 6.4 and 6.0, respectively. Case construction (silk + detritus) was estimated at 256.2 mg AFDW m −2 yr −1 . Production attributable to five food types (animal, vascular plant detritus, amorphous detritus, filamentous algae, and diatoms) was calculated using literature derived values for assimilation and net production efficiencies. Animal food accounted for the majority of B. spinae production (61.71%), followed by amorphous detritus (25.08%). Annual food consumption by B. spinae was estimated at 2158.0 mg AFDW m −2 . Seston data from Dryman Fork and B. spinae consumption estimates were used to calculate seston utilization. While larvae ingested only 0.00007% m −2 of total available summer seston, they selectively captured animal material, consuming 3.5 times the amount entering the study section. These data suggested that the animal component of the seston must be replaced every 400 m to support Brachycentrus feeding alone. While this species exerted a minor influence on seston quantity, its selective capture of high quality animal food could significantly alter seston quality.

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