BLACK GKAIN-STEM SAWFLY. 13 



Measures for control will doubtless be similar to those against 

 Cephus ductus, the western grass-stem sawfly, and Cephus pygmaeus. 



It is obviously impracticable to attack the insect in the egg stage 

 or active larva stage, since both stages occur in the growing grain. 

 The adult can not be reached by any known method. It appears, 

 therefore, that control measures to be successful must either aim at 

 destruction of the hibernating larva or pupa while in the stubble, 

 where the insect passes the greater part of its existence, or be con- 

 fined to cultural methods such as crop rotation. The fact that the 

 larva is located in the part of the stem below the surface of the 

 ground precludes the possibility of accomplishing anything by any 

 ordinary burning of the stubble. Disking the stubble thoroughly 

 as soon after cutting the grain as practicable would possibly be of 

 benefit by turning the infested stubble out and thus exposing the 

 larva to the action of summer heat and winter cold. The larva is 

 quite hardy, however, and only experimentation will prove or dis- 

 prove the effectiveness of disking. 



In Russia plowing down of the stubble as deeply as possible is 

 recommended against this species as well as against Cephus pyg- 

 maeus. The same treatment is recommended and has proved success- 

 ful against Cephus ductus in this country, and it seems the logical 

 treatment for adoption against this species. To be effective the plow- 

 ing must bury the stub containing the larva so deeply that the matur- 

 ing adult will be unable to escape. Shallow plowing will not suffice, 

 as the adults undoubtedly will be able to burrow their way out if 

 covered with only 2 or 3 inches of soil. Deep and clean plowing, 

 therefore, will be essential. The plowing may be done at any time 

 between the cutting of the grain and the following spring prior to 

 emergence of the adults in April or May. 



If, as now seems probable, this insect confines itself, in this coun- 

 try, to the small-grain crops as host plants, there can be little doubt 

 that crop rotation will prove an effective means of reducing damage 

 from it. Wheat, barley, or rye should be followed by some crop 

 which will not serve as a host plant, such as corn or truck crops. The 

 present practice on some farms of growing wheat on the same ground 

 two years in succession is distinctly favorable to the propagation of 

 the pest since the adults upon emerging find themselves surrounded 

 hj ideal conditions for oviposition. The practice also of sowing 

 grass or clover with wheat and allowing the wheat stubble contain- 

 ing the larva to stand undisturbed for two seasons could hardly be 

 improved upon as means of increasing the numbers of this insect. 

 Any system of rotation to be effective should insure thorough plow- 

 ing down of the wheat stubble and the growing of some crop other 

 than a small grain following wheat. 



