24 BULLETIN 841, U. S. DEPARTMENT OF AGRICULTURE. 



species are so numerous in these roadside grasses that it would seem 

 poor policy to recommend the cutting of the grasses in midsummer 

 as a measure of Cephus control. As has been stated, few parasites 

 have been found in stems of wheat, but, without doubt, they will 

 learn very soon of the presence of Cephus in grain fields and will 

 adjust their habits accordingly; 



A braconid, Microbracon cepM, recently described by Mr. A. B. 

 Gahan, 1 also attacks the larvae in grass stems, kills them before 

 maturity, and spins a gray parchment-like cocoon within the gallery, 

 generally near its lower end. This cocoon is truncate at both ends, 

 its disklike extremities completely filling the bore. The adult 

 escapes by biting an opening through the stem in the vicinity of the 

 cocoon. 



ARTIFICIAL CONTROL 



From the foregoing sketch of the life history of the western grass- 

 stem sawfly it seems obvious that this pest will have to be attacked 

 while it is in the larval state. The egg and adult stages are both 

 brief and are clearly beyond the reach of control measures of any 

 sort. For nearly 11 months the insect exists as a helpless larva, 

 protected only by the grass or grain stem within which it lives. If 

 this stem could be destroyed, the larva within would perish. 



The first remedy that occurs to the farmer or the student of field 

 conditions is the burning of the stubble in the autumn or spring. 

 It would seem a very simple matter to set fire to the stubble and 

 destroy at least the majority of the sawfly larvae that are hibernating 

 in it. But when one begins to examine the infested fields it is found 

 that the inhabited stems have been cut at the ground level or below 

 so that it is often necessary to brush away the earth in order to find 

 the stubs containing the larvae. So little heat is generated when 

 stubble is burned that these subterranean steins could not possibly 

 be harmed by the quick passage of the flames. 



In 1907 Mr. Norman Griddle, in Manitoba, wishing to make a 

 thorough test of this particular remedy, spread a layer of straw 

 several inches deep over an infested area in a wheat field and set the 

 straw on fire. More heat was produced than stubble alone could 

 possibly make, the surface of the ground being too warm for the 

 hand after the fire had died down. Even after this severe treatment 

 it was found that, as far as could be learned by a minute search, 

 not a single larva had suffered. They had simply retreated to the 

 lower end of the hibernation cell and "kept cool." 



Another fact must be noted in this connection. When a field has 

 been damaged seriously by the sawfly, the stubble remaining to feed 

 a running fire is of necessity more scanty than in an uninjured field 



1 Gahan, A. B. Description of a new hymenopterous parasite (Braconidm). In Proc. Ent. Soc. Wash., 

 v. 20, no. 1, p. 18-19. Jan., 1918. 



