THE MONTHLY BULLETIN. 



69 



THE WHEAT STRAW WORM. 



{Isosoma giaiidc Kiloy.) 

 By R. W. DoANE, Stanford University. 



California grain fields are not yieldino; as nuicli wheat per acre as tliey 

 used to yield. The principal reason for this is usually, and probably 

 rightly, ascribed to the fact that the soil is becoming depleted by being 

 used for the same crop year after year, often without being plowed 

 deeply enough to ])i'eak up the hard stratum that forms just below the 

 soil that is reached by tlie plow when the field is plowed in the usual 

 way. 



Studies made during the past two years, particularly in the wheat 

 fields in northern California, have shown that another very important 

 factor, and one that has been quite overlooked here, is contributing its 



Fig. 29. — Young wheat showing the effects of the work 

 of the larvEe of Isosoma (jrande. In the middle stalk is 

 an adult just ready to issue. (Original.) 



part toward decreasing the wheat yield. It has long been known that 

 the wheat straw worm, Isosoma grande, occurs in California, but few, 

 if any, have realized its importance here. The insect works in such a 

 way that, even when very abundant and destructive, its presence may 

 readily be overlooked and the damage that it does may be ascribed to 

 other causes. In some fields actual count of hundreds of wheat stems 



