THE WESTERN GRASS-STEM SAWFLY. 5 
sorts provided the stem is sufficiently large for the larval gallery. 
As a rule, the larger, more robust stems are chosen for attack, espe- 
cially in cultivated grasses such as timothy and Bromus. Blue grass 
and similar slender-stemmed species appear to be immune. It is a 
little surprising that a minute examination of Stipa viridula from 
New Mexico developed the fact that none of the stems of this robust 
grass were infested. This Stipa was gathered in northern New 
Mexico, growing in almost the same latitude as the Elymus condensatus 
near Pinto, Utah, where the fly abounds. 
August 25, 1916, the writer, then at Pierre, S. Dak., received 
instructions from the Bureau of Entomology to visit Bottineau County 
Fig. 4.— Wheat field of Thomas Yeam, near Souris, N. Dak., showing heavy damage done by the western 
grass-stem sawfly in 1916. 
in North Dakota and investigate injur}' to wheat. It was believed 
locally that the Hessian fly was responsible for the damage that was 
being done. A very superficial examination of the injured fields 
proved beyond a doubt that the Cephus was present in large numbers 
and was doing an immense amount of mischief. Every field was 
infested, not only in Bottineau County, but in the adjoining counties 
of Benson, Pierce, McHenry, and Rolette. Near Souris, a few miles 
south of the Canada line, a large field of wheat on the farm of Thomas 
Yeam was fairly carpeted with the " straw-fallen"' grain. (See figs. 4 
and 5.) The loss from Cephus injury in this field was estimated at 
60 per cent or more. Six feet of drill row here were taken at random 
and examined plant by plant. Forty-eight infested stubs were found, 
