INSECTS ATTACKING WHEAT. 31 



quito. The sexes pair at once, and the eggs for another generation are 

 laid almost immediately in the field, the adults perishing soon there- 

 after. 



The maggots hatching from these spring eggs go through the same 

 course of development, at the base of the stalk, behind the sheath of 

 the leaf, and do the principal part of the damage noticed in the spring, 

 causing the well-known "crinkling" or falling down of the straw as the 

 wheat heads out. Many of the winged flies of this brood hatch some- 

 time before harvest, beginning to appear, in fact, by the end of May, 

 and these lay eggs at once and give rise to a second spring brood — a 

 fact clearly established this season by breeding experiments at Cham- 

 paign. By harvest practically all are in the so-called "flax-seed" state, 

 and the greater part of them remain behind in this condition in the 

 stubble after the grain is cut. A few, however, are carried away with 

 the straw. From these harvest-time "flax-seeds" the fall generations 

 descend, the first of them appearing either in the volunteer grain or in 

 early-sown wheat, and the second — the hibernating generation already 

 referred to — in wheat of the regular crop. The laying of the eggs for 

 the first of these generations certainly begins by September 1, and ap- 

 parently somewhat earlier. The average length of life of one generation 

 or brood (except the hibernating one), from any stage around to the 

 same stage again, is about six weeks. 



It is, however, a fact of considerable economic interest that this divi- 

 sion into generations is not anywhere complete, but that "flax-seeds " of 

 any generation may lie dormant during the whole life of a generation 

 following, finally hatching with the descendants of their original con- 

 temporaries. Thus, of those "flax-seeds" which form in May and June, 

 some may give the winged fly in June and July, and others not until 

 September; and some of those which form in volunteer wheat in Sep- 

 tember may hibernate and emerge the following spring. 



Remedies. — The United States Entomological Commission, in- 

 its third report ( 1883 ) suggests the following remedies : 



1. There are several destructive Ichneumon parasites of the Hessian 

 Fly, whose combined attacks are supposed at times to destroy about 

 nine-tenths of all the flies hatched. Of these the most important is the 

 Chalcid four-winged fly, Semiotellus destructor, which infests the "flax- 

 seed," and a small parasite of the genus Platygaster. 



2. By sowing a part of the wheat early, and, if affected by the fly, 

 plowing this in and sowing the rest after September 20, the wheat 

 crop may in most cases be saved. It should be remembered that the 

 first brood should be circumvented, or destroyed, in order that a sec- 

 ond or spring brood may not appear. 



3. If the wheat be only partially affected, it may be saved by ferti- 

 lizers and careful cultivation; or a badly damaged field of winter wheat 

 may thus be recuperated in the spring. 



