INSECTS INJURIOUS IN 1902. 5 
litter from the threshing on the field. There is no absolute need 
of burning the straw pile. The flies emerging from ‘‘flax seeds” 
in the center of the pile will never reach the surface. 
4, Since the fly lays its eggs as a rule near the locality 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 possi- 
ble. Varieties of wheat that produce a stout stalk are the least 
affected by this pest. 
5. Co-operation is absolutely necessary, for, however careful one 

Fig. 3.—Cecidomyia destructor (Hessian fly): (a) male; (b) enlarged anal seg- 
ment; (c) head of female; (d) head of male; (e) scale from 
leg of male; (f) scale from wing; all greatly en- 
larged. C. L. Marlatt, U. S. Dept. of Agr. 
Div. of Entomology. 
man may be, if his neighbor is not equally so the latter’s fields 
will afford a supply of this pest for the former. Since this pest 
issues from the ‘flax seed” early in May, a stubble field left for 
corn land and not plowed up to the 10th of May or later has prob- 
ably discharged its quota of flies ready for mischief before plow- 
ing. 
