16 



BULLETIN 841, U. §. DEPARTMENT OF AGRICULTURE. 



these stubs were examined and a number of the inclosed larvge 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 

 larvge 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 crass-stem saw- 1 ,i , i 1 j _ 1 ; r, 



fl y longer than the larva from 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 



