
15 
Natural history and habits.—The Hessian fly is distinctively a wheat 
insect, but will breed also in barley and rye. What has been taken 
for this insect has, in recent years, been found occasionally in timothy 
and several wild grasses, but the insects in these cases are now known 
to be distinct from the Hessian fly, and the occurrence of the latter in 
plants other than those first named is extremely doubtful. 
Over the bulk of the wheat area of the United States there are two 
principal broods of the Hessian fly annually, viz, a spring and a fall 
brood. There are, however, supplemental broods, both in spring and 
in fall, particularly in the southern wheat areas, but in the extreme 
northern area of the spring-wheat belt there may be only a single 

Fic. 6.—Hessian fly (Cecidomyia destructor): a, female fly; b, flaxseed pupa; c, larva, d, head and 
breastbone of same; e, puparium; f, cocoon; g, infested wheat stem showing emergence of pupze and 
adults (original). 
annual brood, the progeny of the spring brood passing the late sum- 
mer and the winter in the flaxseed state instead of developing a brood 
in autumn. It is possible, however, that in this region an autumn 
brood may develop in volunteer spring wheat. 
Each generation is represented by four distinct states, viz, (1) egg, 
(2) maggot, or larva, (3) pupa, or flaxseed, and (4) matured winged 
insect. 
The eggs are very minute and slender, pale red in color, and are 
usually deposited in regular rows of 3 to 5 or more on the upper 
surface of the leaf. In the case of the spring brood they are some- 
times thrust beneath the sheath of the leaf, on the lower joints. The 
number of eggs produced by a single female varies from 100 to 150. 
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