24 THE HESSIAN FLY IN THE UNITED STATES. 
mating the damage as high as 25 per cent in some places, and at from 
5 to 10 per cent of the entire crop, he says : 
In Southern States this insect is double brooded and hibernates in the "flaxseed" 
stage in winter wheat, volunteer wheat, and in other plants, including, possibly, 
some of the larger grasses. But this is their habit only in the South. Here the 
insect must lead a different sort of a life, for instead of being double brooded it is 
single brooded. This could be expected from the conditions prevailing in the 
greater part of the State, but we have had no proofs thus far. Of all the infested 
stalks gathered as soon as the injury became visible, not a single Hessian fly has 
issued, and numerous puparia (the " flaxseed" stage) are still unchanged in the 
breeding cages. This assuredly seems to indicate that the flies do not issue during 
the autumn, as they do farther South, but remain in the culm until spring. Another 
proof, though not a safe one to depend upon, is the fact that no larv* or puparia 
could be found in the volunteer plants of wheat growing near fields that had been 
badly infested. The many puparia kept in properly constructed breeding cages 
gave forth, however, very large numbers of parasites. Three different species were 
raised, and in such numbers that in some cases nearly all the Hessian flies had been 
destroyed in the puparia. 
For all of the material collected in 1897 the failure to produce adults 
was fully as manifest, and it seems to me that in many cases the retar- 
dation amounted simply to the death of the insect. Even when not 
producing parasites the puparia have failed to produce adults, and it 
would seem that the process of desiccation had gone to the point of 
destruction before conditions permitted the development of the insect. 
In many cases the puparia were shriveled and gave evidence of incom- 
plete development, and I suspect that in many cases the straw had 
ripened and cut off their nutriment so early as to prevent maturity. 
This might easily occur if the adults emerged and deposited eggs a 
little late in spring. The occurrence of a cold, late spring would here 
favor the retardation of emergence of the adults and allow such maturity 
of the wheat as to largely prevent development of larva?, and as such 
conditions are of frequent recurrence in this region there would seem 
to be in this a natural check on the species that may be sufficient in 
general to limit the insect to harmless numbers. 
I have, on the other hand, seen the early maturity of Hessian flies in 
breeding cages ; as infested wheat sent me by Professor Webster during 
the past winter produced flies emerging from March 4 to 7, and speci- 
mens of puparia kept in an office room before being sent to me emerged 
still earlier. 
With the amount of evidence that has now accumulated there seems 
no longer any possibility of questioning the acceleration and retardation 
of the insect for conditions of latitude and of climatic variation within 
the same locality. Further, it appears to me that we have sufficient 
evidence to conclude that the conditions affecting this acceleration or 
retardation are temperature and moisture, and that with a knowledge 
of these conditions it should become possible for the intelligent culti- 
vator to foresee the occurrence or absence of the pest to such an extent 
as to adapt his agriculture to the avoidance of their injury. The 
methods for such adaptation naturally fall under the discussion of 
remedies. 
