16 
BULLETIN 841, U. S. DEPARTMENT OF AGRICULTURE. 
these stubs were examined and a number of the inclosed larvae were 
found to be still living, active, and unchanged. Four months later, 
17 months from the time they were gathered, they were still alive 
and feebly active. Infested stubs of the same grass taken during 
September, 1912, and treated in the same manner, contained at least 
one living larva on February 23, 1916, 3 years and 5 months later. 
The others had nearly all died within about 30 months of the time 
they were gathered. It is possible that the lack of necessary moisture 
may account for the retardation of these captives. However, the 
same retardation of development has been noted in the field. Inhab- 
ited stubs of the previous year's 
growth of grass and grain not infre- 
quently have been found, containing 
larvae that were to all appearances 
entirely normal and active. It ap- 
pears more than probable that in this 
manner the perpetuation of the spe- 
cies is assured in case of unfavorable 
seasons. 
During the winter the larvae are, 
of course, frozen, or are chilled into 
immobility and show no signs of life 
when disturbed. As soon as the earth 
warms in the spring they again grow 
active and move freely up and down 
within the limits of the silk-lined 
hibernation chamber until the time 
of pupation arrives. 
THE PUPA 
The pupa when first formed is 
fig. 11— stems of wheat grooved intemaiiy milk- white, slender, and somewhat 
by larvae of the western grass-stem saw- i()nger than ^ ^^ frQm which 
it was derived. Its average length 
is not far from 12 mm. and its breadth is about 1.5 mm. At first 
the pupa lies motionless within the silken pupation chamber or 
cocoon (fig. 12) for probably a day or two, after which inactivity it 
again becomes animated. When disturbed it will endeavor to escape 
the threatened danger by moving either up or down the tube, hitch- 
ing itself along in much the same manner as the larva but going a lesser 
distance with each effort. Like the larva it is almost always found 
with its head pressed closely against the plug of frass at the upper 
end of the chamber. In a few cases pupae have been discovered 
heading downward in the stem. It is doubtful if these can reverse 
