110 
Mary Beth Roush and Donald C. Tarter 
40 
30 
20 
10 
0 
>- 
u 
z 
10 20 30 40 
BODY LENGTH mm 
Fig. 1. Length-frequency histograms at seasonal intervals of P. postica larvae 
from Greenbottom Swamp. M = March, D = December, N = November, and 
number = sample size. 
months. Wiggins (1973) reported living, first-instar, phryganeid larvae (of 
unknown genus), still within a gelatinous matrix, beneath wet leaves in a 
pool basin in Algonquin Park, Ontario in October 1960. Wiggins (1977) 
reported final instars of P. ocellifera in a littoral region of a British 
Columbia lake from November to June. 
Larval case length also showed seasonal variation (Fig. 4): fall 
(November) x = 23 mm, R = 18-33 mm; winter (December) x = 39.3 mm, 
R = 22-55 mm; spring (March) x = 50.0 mm, R = 33-69 mm. The correla- 
tion between case length and body length was high in fall (Y = 11.65 + 
0.86X, r= 0.72) and winter (Y = -10.61 + 2.25X, r= 0.87) (Fig. 5), but low 
in spring (Y = 27 + 0.74X, r = 0.37). In these equations, Y = case length 
(mm) and X = total body length (mm). These data indicate that body 
length and case length are closely related in fall and winter, but in spring 
case construction continues as larval growth slows down. 
Once the larva of P. postica has begun to add a new ring at the anterior 
end of the case, it completes this addition rather rapidly, often with 
segments of the same leaf. The larva may pause for several days, or even 
SPRING M 
43 
