16 
The whitish maggots hatch in from three to five days and crawl 
down the leaf to the base of the sheath, embedding themselves between 
the sheath and stem, and develop on the substance of the wheat, caus- 
ing more or less distortion and bulbous enlargement at the point of 
attack (figs. 6, 7). 
In a few weeks the larva contracts into a flaxseed-like object, which 
is the puparium. In the case of the spring brood the insect remains 
in the flaxseed state during midsummer, yielding the perfect insect for 
the most part in September; in the case of the fall brood the winter is 
passed in the base of the wheat in the flaxseed condition. 
The fall brood works in the young wheat very near or at the surface 
of the ground. The spring brood 
usually develops in the lower joints 
of the wheat, commonly so near the 
ground as to be left in the stubble 
on harvesting. With spring wheat 
the attack is sometimes just at the 
surface of the ground, as in the case 
of the fall brood. The adults from 
the wintered-over flaxseed puparia 
emerge during April and May, most 
numerously before the middle of 
the latter month. The adults of the 
important fall brood emerge chiefly 
during September. 
There is a supplemental spring 
brood following the main one and a 
supplemental fall brood preceding 
the main one. ‘These supplemental 
= broods are, as a rule, comparatively 
Fie. /.—Wheat plant showing injuries by Hes- ynimportant, most of the individuals 
sian fly: a, egg of Hessian fly; b, larva; ~ , : 
¢, flaxseed: d, pupa, or chrysalis; ¢, female, ©1 the spring and fall breedsvaome 
natural size; f, female; g, male; h, flaxseed through the course of development 
between the leaves and stalk; 7, chalcidid ‘ i 
parasite—all enlarged except wheat stem and first indicated. Under any favorable 
fig. ¢ (after Riley, Burgess, and Trouvelot). weather conditions, as indicated fur- 
ther on, the supplemental fall brood may become a very important one, 
as illustrated by the season of 1899-1900 in the Ohio valley. 
Exceptionally also, this insect may remain dormant in the flaxseed 
state for a year or more and still bring forth the adult, a provision of 
nature which is doubtless intended to prevent the accidental extermina- 
tion of the species. The migrating and scattering brood of adults is 
the one developed in the fall; the spring brood is less apt to scatter 
from the field in which it is developed. 
The important feature in the life history of the Hessian fly from the 
standpoint of control is the time of emergence of the fall brood or 
132 

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