316 
Psyche 
[September-December 
observed. On May 1 1, at a temperature of 20 C, the first exuviae 
(19) were found at the water line and up to four feet on the wall 
of the bridge. One adult female was found parasitized in a spider’s 
nest. The peak of emergence was on May 12 when 31 exuviae 
and three females were collected. From May 13 through 19, 51 
exuviae were collected from the wall of the bridge. 
Minshall and Minshall (1966) found the adults of Isoperla 
clio and Isogenus decisus emerged between 4:30 and 6:30 PM. 
Minshall and Minshall (1966) stated they found Isoperla clio 
exuviae several meters away from the stream, with the first adults 
collected in April, then a few in June, with a peak in April. Ac- 
cording to Harper (1973), /. clio adults emerged on May 17 and 
lasted 20 days. He also reported on other setipalpian Plecoptera 
and the emergence patterns are all similar. 
The direct count of ovarian eggs of fifteen females (only eight 
contained eggs) resulted in a range of 4 to 60 eggs per female; 
the mean was 30. Seven of the females examined had ovaries 
containing undeveloped eggs or none at all. The eggs of D. robusta 
are spindle shaped and light, golden-brown color. 
Twenty percent of the eggs from eight females had a range 
of 0.28 to 0.43 mm (x = 0.39) in length and 0.21 to 0.32 mm (x = 
0.27) in diameter. 
The months of May through July for two summers revealed 
no naiads in the stream. At this time, the stream was dried up 
and possibly the eggs of D. robusta were diapausing for 12-14 
weeks. The rains of August caused the stream to be normal again 
and at this time the naiads, very small in size, reappeared. 
Under laboratory conditions, Miller (1939) reported that the 
eggs of Pteronarcys (- Allonarcys) proteus Newman diapaused 
from 305 to 325 days. Diapause was apparently not obligatory 
since hatching was forced by high temperature. Harden and 
Mickel (1952) reported that the eggs of Isoperla bilineata (Say) 
oviposited in June and maintained in the laboratory did not 
hatch until October. The eggs of I. clio apparently hatch in 
August and September (Minshall and Minshall, 1966). 
The chi-square test indicated a significant departure from 
the 1:1 ratio at the 0.05 confidence level. The sex ratio was based 
on a laboratory reared sample of 8 males and 15 females, a ratio 
of about 53 males to 100 females. 
