22 
BULLETIN 841, I T . S. DEPARTMENT OF AGRICULTURE. 
in a cell hollowed in the solid parenchyma of the stem of Elymus 
condensatus, this cell being a little larger than the egg. Besides 
piercing the stem, the saws are also of use in excavating this egg cell, 
in case such a cell is needed. At Kimballs near Salt Lake City, in the 
same grass, the eggs were nearly always placed in the hollow part of 
the stem, lying free in the central cavity. 
Normally but one egg is placed in each stem. However, no atten- 
tion is paid to previous oviposition and as many as five eggs have been 
taken from a single stem. As is stated elsewhere, only one of these 
larvae can possibly survive until fall, so this multiplication of eggs 
simply means economic waste for the Cephus. 
The date of ovipo- 
sition varies with the 
latitude and the alti- 
tude. At Pinto, Utah, 
on the edge of the des- 
ert country and with 
a low altitude, newly 
hatched larvae were 
found June 14, 1912, 
while at Kimballs, 350 
miles north of Pinto 
and with an altitude 
of 7,000 feet, oviposi- 
tion was beginning 
during the first week 
of July m the same 
year. 
Air. Criddle states 
that in Canada most 
Fig. 15. — Life-history diagram of the western grass-stem sawfly. „ . , 
oi the eggs 'are depos- 
ited during June. The date of oviposition in the Dakotas and in 
Minnesota is unknown. (Fig. 15.) 
KEY TO THE NORTH AMERICAN SPECIES OF CEPHUS 
Through the courtesy of Air. S. A. Rohwer of the Bureau of Ento- 
mology a key for the determination of the known species of the genus 
Cephus occurring in North America is here presented. 
Stigma and costa dark brown of a unif orm color ; mesepisternum black ; femora black ; 
apical tergite and venter black ; face and scutellum black (face of male ■with yellow 
spots) pygmaeus Linnaeus. 
Stigma in greater part and costa yellow ; mesepisternum with the upper angle yel- 
low; apical tergite and usually the venter in part yellow; femora usually mostly 
yellow; face and scutellum of female usually black but occasionally with yellow 
spots ductus Norton. 
