
19 
such as was experienced in the Ohio Valley in the fall of 1899, will retard 
the development of the Hessian fly; but a week or ten days after a 
drenching rain, following such adry spell, flies will come forth from 
the flaxseed stage in numbers. All of these conditions, therefore, 
must be borne in mind in attempting to determine when it is safe to 
sow winter wheat, and when the conditions are very unfavorable it will 
probably be wiser to plant other crops than those which the Hessian fly 
infests, as indicated in the consideration of preventives and remedies. 
Effect on wheat.—The first indication in the fall of the presence of 
the fly in wheat is the much darker color of the leaves and the ten- 
dency to stool out rather freely. This is very noticeable, and gives 
the wheat for the time being a very healthy appearance. The leaves 
are also broader, but the upright central stems are wanting, having 
been killed by the fly. Later, the infested 
plants turn yellow or brown and die in part or 
altogether. 
The spring brood of larve attacks tillers 
or laterals that have escaped the fall broods, 
dwarfing the stems and weakening them so 
that they usually fall before ripening and. can 
not be successfully harvested. 
The excessive stooling, or tillering, of wheat 
attacked by the fly is doubtless due to the nat- 
ural tendency on the part of the plant to offset 51. 4 srosian BE ae ee 
the injury by forming new lateral stems, and destructor): a, egg; b, larva 
therefore a wheat that has a natural tendency es cares eth aete ae 
in this direction is less apt to be seriously dam- —ments—a, 5, enlarged; ¢, 4, 
aged by the fly. Other things being equal, 2°?" “arsed (original). 
also, wheat with stiff, flinty stems is less damaged by fly attack, chiefly 
because the straw does not bend or break so readily at the point 
weakened by the spring brood of larve. 
Natural enemies.—The Hessian fly in the larval and pupal periods is 
subject to the attacks of important natural parasites—small four- 

winged flies which develop within the bodies of their hosts. There 
are several native parasites, and in Europe there are many others, one 
of which is remarkably prolific, and the Department has attempted 
its artificial introduction into this country. This species, Zntedon 
epigonus, has been liberated in several States, and seems to have 
obtained a foothold, and considerable good may be expected from it. 
In general, the parasites are effective only in limiting damage and 
are useful where other preventives are neglected, but can never take 
the place of active measures where perfect immunity is desired. 
132 
