|Abstract or Summary
- The role of detritivores in the conversion of allochthonous
leaf material in two small streams in the Cascade Range of Oregon
was studied. Their importance in relation to other consumers was
estimated from emergence and benthic standing crop data.
Ingestion rates and efficiencies of utilization of bigleaf maple
(Acer macrophyllum) and red alder (Alnus rubra) leaves by several
species of stream detritivores, one species of stonefly and several
species of caddis lies, were measured under field or laboratory conditions.
Mean consumption rates varied from 0. 04 mg/mg/day for
Halesochila taylori larvae (Trichoptera:Limnephilidae) feeding on
maple leaves to 0.60 mg /mg /day' for Lepidostoma sp. larvae
(Trichoptera :Lepidostomatidae) feeding on alder and maple leaves.
Ecclisomyia sp. larvae (Trichoptera:Limnephilidae) consumed 0.10
mg/mg/day of maple leaves in the field. All consumption rates were calculated assuming constant feeding rates by the insects and
constant rates of leaf decomposition without insects, but a model is
discussed that allows non-linear feeding and leaf decomposition
Efficiency of food utilization was measured either as assimilation
efficiency, the ratio of assimilated food (ingestion minus egestion)
to consumption; or as gross growth efficiency, the slope of the
growth:consumption line calculated by linear regression analysis.
Assimilation efficiencies ranged from 7.4% for Heteroplectron
californicum larvae (Trichoptera:Calamoceratidae) fed on maple
leaves to 12% for Lepidostoma sp. larvae fed on alder and maple
In order to assess the role of microbial communities in leaf
utilization by Pteronarcys princeps (Plecoptera:Pteronarcidae),
nymphs were fed untreated maple leaves and maple leaves treated
to reduce bacterial or fungal populations, for a period of 54 days.
Gross growth efficiency when fed on untreated leaves was 4.94%
compared with 1.03% for the insects fed antibacterial treated leaves.
When fed fungicide treated leaves, the mean consumption rate was
less than 10% of the consumption of untreated leaves and mortality
was 85% compared with 15% for the insects fed untreated leaves. It
was concluded that bacteria play a major role in the utilization of
leaves by Pteronarcys princeps and that fungi are important as astimulus to feeding, although they may also aid in utilization of the
To aid in classifying the emergence and benthos data into
trophic categories, an extensive literature review of the foods of
aquatic insects was compiled. The estimated yearly emergence of
aquatic insects from Watershed 10 was 81 mg/m² /yr. of algivores,
253 mg/m²/yr. of detritivores, and 135 mg/m²/yr. of carnivores.
The mean standing crop of aquatic insects in an old-growth location
in Mack Creek was 0.85 g/m² of algivores, 3.10 g/m² of detritivores,
and 2.31 g/m² of carnivores; and 0.83 g/m² of algivores, 1.57 g/m²
of detritivores, and 4.04 g/m² of carnivores in a clear-cut location.
A model is included describing the cycling of energy within
the detrital component of the stream system, reflecting the importance
of the fecal material and leaf fragments that return to the