THE WESTERN GRASS-STEM SAWFLY. 25 



and consequently it would be exceedingly difficult to burn such a 

 field even under the most favorable conditions. 



In Utah the bunch grass, Elymus condensatus, is much infested 

 by this same fly and frequently is burned by fires that sweep the 

 mountain side. This Elymus forms dense sods, with stems often 

 more than 3 feet in length, and the heat from its combustion is great. 

 The writer has examined a large series of burned sods and has seldom 

 discovered any injury to the larvae from the fire. 



These facts would indicate the futility of burning the stubble as 

 a control measure. 



Although it might seem possible to decrease the numbers of the 

 fly by mowing roadside and fence-row grasses during July, thus 

 destroying the larvae always present in the stems of these grasses, 

 careful study has proved that a large percentage of the larvae in 

 these grasses is parasitized and therefore it would seem unwise to 

 take steps that might diminish the number of parasites. Without 

 any doubt grain fields in North Dakota and Canada are invaded 

 regularly by sawflies that issue from grass growing along their borders. 

 Still, because of the multiplication of useful parasites from this same 

 grass it is probably inadvisable to mow the grass in midsummer. 



Deep plowing, 5 to 6 inches, is perhaps the best remedy for the 

 sawfly that can be suggested at present. It is much easier to 

 advise this than to put it in practice. In almost every plowed field 

 in any part of the country each furrow is marked by a row of stubble 

 projecting from the inner edge of the furrow slice. Unless the stubble 

 is turned squarely upside down, burying it at least 5 inches, the 

 resulting surface at the same time being compacted by harrowing or 

 rolling, the flies will be able to escape with ease from beneath the 

 ground. 



In the fall of 1916 the writer buried four lots of infested stubble in 

 different depths of earth sifted and compacted by jarring. These 

 were buried, one at 3 inches, one at 4, and 2 at 6 inches, in glass jars, 

 10 stubs in each of the first two, 20 in the other two. August 6, 

 1917, these cages were examined with results as follows: 



Under 3 inches of earth all adults emerged. 



Under 4 inches 1 larva died, all others emerged. 



Under 6 inches 1 adult died in the cell, 6 larvae also died, 2 active 

 living larvae still in the cell, all other adults emerged. 



Under 6 inches 7 larvae died in the cell, all other adults emerged. 



Lumpy soil in the field might make it easier or harder for adults to 

 emerge than fine soil in a jar, and this point might be difficult to 

 determine. 



Cultural conditions in North Dakota are not favorable for burying 

 the stubble by plowing. Spring wheat is followed in many cases by 

 winter rye which is disked into the wheat stubble after harvest. This 



