6 BULLETIN' 841, IT. S. DEPARTMENT OE AGRICULTURE. 



an average of eight to each foot of drill row. This would mean 150 

 to the square yard or about 726 ; 000 larvae to the acre. Higher counts 

 were made later in this same field, so the averagemay be larger than sta- 

 ted. During April, 1917, Mr. Yeam's field was again visited and a ran- 

 dom square yard marked out and counted. Two hundred and sixty-nine 

 infested stubs were taken from this yard, which would mean more 

 than 1,300,000 larvae to the acre. Fifty of these stubs were opened 

 and 47 of the imprisoned larvae that had spent the winter within the 

 straw were found to be normal and very much alive. The proportion 

 of living individuals among the hibernating larvae seldom falls below 

 this ratio. 



: 



Fig. 5.— Bird's-eye view of wheat in Thomas Yeam's field, Souris, N. Dak. Ninety per cent of these fallen 

 wheat stems have been mined by the western grass-stem sawfly. 



The spring of 1917 witnessed a peculiar condition of things in 

 Bottineau and the adjoining counties of North Dakota. The dry 

 weather hindered the growth of both grasses and grains, so that when 

 the adult Cephus began to appear in June there was almost no oppor- 

 portunity for oviposition. Stems of Bromus from chance sods grow- 

 ing among wheat and on waste ground were filled with eggs. Young 

 plants of spring wheat that had barely begun to joint were attacked 

 and often contained as many as three and four eggs placed in the 

 stem close to the ground. With a few strokes of the net 136 adults 

 were swept from young wheat, so numerous were the flies at that time. 

 In spite of the unfavorable oviposition conditions of that spring, the 



