u 



DIPTERA OF MINNESOTA. 



4. Since the fly lays its eggs, as a rule, near the locaHty where 

 it emerges from the "flax seed," it is best not to plant wheat on the 

 same ground two years in succession where rotation is possible. Vari- 

 eties of wheat that produce a stout stalk are the least affected by this 

 pest, and varieties of wheat should be selected and the soil handled to 

 that end, remembering that a rank growth does not mean strong straw, 

 but the contrary. 



5. Co-operation is absolutely necessary, for however careful one 

 may be, if his neighbor is not equally so, the latter's fields will afford 

 a supply of this pest for the former. Since the pest issues from the 

 "flax seed" early in May, a stubble field left for corn land not plowed 

 up to the loth of May or later has probably discharged its quota of 

 flies, ready for mischief, before plowing. 



Fig. 51. A Pine cone willow gall 

 caused by a Cecidomyid. Original. 



Fig. 52. The gall shown in Fig. 51 

 opened, showing maggots. Those 

 in the center are the gall makers. 

 Original. 



As stated elsewhere, this pest will increase and decrease at regular 

 intervals, due to the increase and decrease of its many parasites, 

 which in turn are due to the abundance or the contrary of the fly. 

 Regarding the number of broods of Hessian fly in Minnesota, bear- 

 ing in mind the fact, as clamed, that the pupa may live many months 

 in its case before emerging as a fly, we hardly feel justified in claiming 

 a number of broods of this pest each season, until further observations 

 have been made along this line. 



The Wheat Midge, Diplosis tritici, another pest of this family, 

 works in the flowers of the wheat. Another species of the same 



