210 
Psyche 
[June-September 
mud and debris in the net. The larval alderflies were collected and 
preserved in 70 percent ethanol. 
Temperatures were taken with a Taylor maximum-minimum 
thermometer placed on the pond bottom 0.5 meter below the water 
surface. They were recorded in degrees Celsius once per month at 
the time benthic samples were taken. Water chemistry tests were 
performed in the field with a Hach chemical kit, Model AL-36- 
WR. All tests were completed within one hour. Hydrogen-ion 
concentration (pH) was measured colorimetrically. Dissolved oxy- 
gen, carbon dioxide, hardness (magnesium and calcium), phenol- 
phthalein and methyl orange alkalinity, free acidity, and total 
acidity were measured and recorded in mg/1. 
Size classes were determined by length frequency distributions 
arranged in 1 mm length groups. Total length (exclusive of the 
caudal filament) was measured under 7X magnification with calipers 
and a plastic ruler (nearest 0.5 mm). Head width was measured with 
an ocular micrometer between the inner edges of the eyes (nearest 
0.01 mm). Differences in head width of 124 larvae were determined 
to show the mean, range and standard deviation. 
A total of 84 foreguts were examined to determine food habits. 
The head was removed and the abdomen was split open to remove 
the intestine. The contents of the intestine were removed and 
examined under a dissecting microscope and a compound micro- 
scope to identify their contents. The percent frequency of occur- 
rence of each item was determined, and the monthly and seasonal 
averages and various sizes were compared. 
For the pH tolerance test, forty mature larvae collected from the 
pond in April were taken to the laboratory for acclimatization over 
a 24 hr period. The larvae were placed in groups of 10 in 4 finger 
bowls. One bowl was filled one-third of the way with pond water. A 
one molar solution of potassium dihydrogen phosphate (KH 2 P0 4 ) 
was diluted approximately into the other three bowls, to set pH 
values at 5.5, 4.0, and 2.5. The pH value of the control was 7.0. A 
Model 5 Corning Scientific pH meter was used to determine pH 
values. Oxygen was constantly supplied with air stones. The temper- 
ature did not change significantly during the experiment and 
averaged 12 C. The 96 hour TL m (median tolerance limit) test 
(APH A, 1965) was used to measure the effect of low pH. The pH 
value at which 50 percent of the alderfly larvae died after 96 hours 
was determined by straight-line graphical interpolation. 
