149 
believe the winter season will be found to be shorter and the summer sea- 
son lengthened until they become equal, while to the north I confidently 
look for the autumn season of activity to wholly disappear and the 
species found to be single brooded. (See Fig. 3.) 
Heretofore we have told people that the fly could not exist except 
where fall wheat was grown. But this can be said no longer, as the 
pest occurs in North Dakota and in a locality where fall wheat is never 
sown. As the fall brood of flies emerges continually earlier as we go 
northward, it seems to me that we must eventually reach a point where 
it will cease to appear in autumn at all, and go over until spring, a 
state of affairs that will easily account for the breeding in spring wheat 
N^O^S, Aa.Jq J. M. A. 
IG. 3.— Illustrating the divergence of the two annual broods of the Hessian Fly 
and latitude (Webster del.). 
"ith reference to date 
in North Dakota. In other words, I expect to find that nature has 
protected the species alike from the protracted northern winter, and 
the equally prolonged southern summer, by varying its resting season 
with the latitude, and, possibly, also with its proximity to the seacoast. 
That is, we shall find the insect passing both the hot and cold seasons 
largely in the flaxseed stage, that being the stage of development during 
which it is best protected from the elements and lack of food. 
There are several good reasons why we might expect the fall brood 
to become extinct to the north, while the spring brood continues, the 
principal one being that there is not sufficient time for the former to 
develop before the cold season begins. Besides, in the continuity of the 
species it can best be spared, and I understand it is not present in Eng- 
land. In nearly all cases where a species is two-brooded, the spring- 
