Head Width, mm 
58 
3— 
2 — 
1 — 
J 
Month 
Figure 2. Population range diagram showing monthly head width variations in 
B. bajkovi nymphs. Beech Fork of Twelvepole Creek, Wayne County, West Virginia, 
1976-77. Vertical lines = range, horizontal lines = mean, open rectangles = one 
standard deviation, dark rectangles = two standard errors of the mean, numbers = 
sample size, f = females, m = males. 
known to what extent they may be a part of the regular diet or 
ingested accidentally along with other food items. The most noticea¬ 
ble monthly variations in diet composition were the increase in plant 
detritus during the fall months, probably due to the large amount of 
leaves in the stream, and the increase in the abundance of diatoms in 
the spring months. 
Nymphs of other mayfly species feeding on plant detritus, dia¬ 
toms, and algae have been reported by Minshall (1967), Pescador 
and Peters (1974), Richardson and Tarter(1976), and Hamilton and 
Tarter (1977). 
Nvmphal Sex Ratio. The chi-square test on B. bajkovi nymphs 
showed no significant departure from the 1:1 sex ratio at the 0.05 
confidence level. The test was applied to 163 males and 179 females 
collected from August through May. The July nymphs were too 
small to sex. 
Adult Stage. Last instar B. bajkovi nymphs with wing pads 
developing were first collected from the stream April 26, and the last 
