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Psyche 
[Vol. 92 
Results and Discussion 
Water Quality. Dissolved oxygen concentration ranged from 8 
(May and July) to 13 mg/1 (December); the mean was 11.0 mg/1. 
The mean hydrogen ion concentration (pH) was 8.5; a range of 7.0 
(June) to 10.0 (August). The carbon dioxide level was 0.0 mg/1 
during all months except August (15.0). Total hardness ranged from 
34.2 (December- April) to 102.6 mg/1 (August); the mean was 48.5 
mg/1. The mean annual water temperature during the study period 
was 9.8 C; the range was —1 (December) to 19.0 C (May, June, 
September). 
Nymphal Stage 
Foregut Analysis. The nymphs are detritivorous with 68.5 
percent of the diet composed of plant detritus. Plant detritus was 
greatest during the months of December through May. Mineral 
detritus, probably ingested^ accidentally, was regularly observed in 
the foregut every month (X = 21.7%). Diatoms, usually Cymbella 
and Navicula, comprised 8.9% of the diet. They increased during the 
months of July through October. Filamentous algae, mainly 
Oedogonium and Oscillatoria, made up about one percent of the 
diet. 
Chaffee and Tarter (1979) noted that the nymphs of B. bajkovi (= 
lacustris) are detritivorous with 65.3 percent of the diet composed of 
plant and leaf detritus. The nymphs of B. berneri are detritivorous 
with 74.5 percent of the diet made up of organic and mineral detri- 
tus (Morris et al., 1980). 
Development. Monthly length-frequency histograms indicated 
a one year (univoltine) life cycle (Figure 1). The smallest nymph (1.3 
mm) was collected in September and the largest nymph (10.9 mm) 
was collected in late April. 
Univoltine life cycles were reported for B. rogersi (Pescador and 
Peters, 1974), B. berneri (Morris et al., 1980) and B. bajkovi (= 
lacustris) (Chaffee and Tarter, 1980). 
The monthly progression of mean head widths for male and 
female nymphs is illustrated in Figure 2. Male nymphs showed the 
greatest growth in April (28%) and July (27%). Female nymphs 
showed the greatest growth in April (16%) and July (34%). Little or 
