22 



BULLETIN 841, U. 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 larva? 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 in the same 

 year. 



Mr. Criddle states 

 that in Canada most 



Fig. 15. — Life-history diagram of trie 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 Mr. 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 uniform 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. 



