NATURAL ENEMIES. 27 
each case may be desirable, we have the general fact that throughout 
an immense territory in the United States where wheat is grown in 
close proximity to oats, timothy, and other grasses, we have never had 
a record'Of the Hessian fly's attack upon these crops. 
In any deductions, therefore, relating to the control of the Hessian 
fly, it may be considered for all practical purposes that the insect lives 
only on wheat, rye, or barley, and will not perpetuate itself on other 
plants. 
EFFECT UPON THE PLANTS. 
The attacks of the Hessian fly upon the plants produce very char- 
acteristic effects, generally so distinctive that the appearance of a field 
will at once indicate to a practiced eye the presence of the pest. The 
effects differ with the season, perhaps, more properly, with the stage of 
growth of the wheat plant at the time of attack. 
In autumn the eggs are laid upon the early appearing leaves and the 
passage of the larvae down the sheath carries them down to or below 
the surface of the ground, often very near to the root itself. Here their 
presence causes more or less swelling of the base of leaf and culm, 
scarcely enough to be counted a gall formation, but the immediate 
effect seems to be a stimulus at the point of attack. Indeed, as Webster 
has pointed out, the affected plants present a darker green color, which 
has been recognized by farmers as indicative of Hessian fly attack, 
this color to be followed later by a brownish and then a yellowish 
color for the infested tillers. If the plant is attacked early and fails to 
tiller, the result is death of the whole plant; if tillers have already 
formed, the larva' may enter but one or part of them, and the others 
may develop into healthy stalks and furnish the basis for a crop. 
The attack in spring being made usually after the stalks are well 
formed, the eggs are placed on the lower leaves, and the larvae, as a rule, 
will be found just above the first joint. Their presence here so weakens 
the stalk that it bends over, the upper part of the stalk falling to a 
horizontal position and at right angles to the base. The appearance of 
these fallen stalks is particularly characteristic, and an examination 
will bring to view the larvae or puparia just below the bend and above 
the lower joint. Rarely the larvae may occur above the second or third 
joint, and it is stated that sometimes they pass below the ground, as 
with the autumn brood, and in such case the stalk falls by breaking at 
the surface of the ground. These tacts have a value not only as a 
means of distinguishing the Hessian fly from other wheat pests, but it 
can easily be seen that the position of tin 4 larva 1 mast be a determining 
factor in the adoption of certain measures of control. 
NATURAL ENEMIES OF THE HESSIAN FLY. 
The importance of the parasites of the Hessian lly is probably hard 
to overestimate, since to this factor we have doubtless to refer the 
usual scarcity of the insect. This may be inferred, in part, from 
