THE WESTERN GRASS-STEM SAWFLY. 



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 Yearn, near Souris, N. Dak., showing heavy damage done by the western 



grass-stem sawfly in 1916. 



in North Dakota and investigate injury 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 

 Yearn 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, 



