17 
broods of adults. This arises from the fact that the chief means of 
preventing loss from this insect is in sowing late enough in the fall to 
avoid infestation. For the average season or normal conditions dates 
at which sowing is comparatively safe have been determined for the 
principal winter-wheat districts. For example, the dates after which 
sowing may be safely undertaken in the State of Ohio, as shown by 
the very careful investigations of Professor Webster, vary over a 
period of at least a month from the northern latitudes of the State to 
the southern latitudes, or from approximately September 10, in the 
north, to October 10, in the south. Wheat sown after the dates men- 
tioned, or after intervening dates for intervening latitudes, will germi- 
nate in normal seasons after the Hessian fly has disappeared and be free 
from attack. 
The question of latitude, however, is not the only one to be consid- 
ered, since temperature is affected also by altitude, and in mountainous 
States like West Virginia, as shown by the very careful studies of Dr. 
Hopkins, the altitude must be taken into consideration in determining 
the proper date for planting. The normal safe date for planting must 
be determined for each locality separately. Ohio farmers are referred 
to Bulletin No. 119 of the Ohio Experimental Station, by F. M. Web- 
ster, and West Virginia farmers to Bulletin No. 67 of the West Virginia 
Experimental Station, by A. D. Hopkins. 
Unfortunately, also, it is not possible to give a uniform date for 
seeding which may be relied on year after year. The extraordinary 
development of the Hessian fly and the serious consequent losses to the 
crop of 1899-1900 have emphatically demonstrated this fact. The 
loss from the Hessian fly for the crop mentioned has been one of the 
worst in the history of this insect in America and probably amounted 
to fully 80 per cent of the normal yield throughout the infested 
region (fig. 8) which covered the main winter-wheat districts of the 
Ohio Valley and amounted to a loss of from thirty-five to forty millions 
of dollars worth of grain. The extraordinary multiplication of the 
fly for the season indicated resulted from an unusual scarcity of the 
parasitic enemies of the insect and a series of very favorable weather 
conditions, the latter, as indicated by Professor Webster, being the long 
drought of the autumn of 1899 which prevented the normal early 
hatching of the Hessian fly, and the mild autumn and winter following 
which enabled the insects to continue breeding and ovipositing much 
later than is ordinarily the case, so that few fields escaped fall infesta- 
tion. <A favorable winter carried these insects through safely, and the 
enormous number of flies which emerged for the spring brood resulted 
in all late-sown or other fields which had escaped the fly in autumn 
being infested by hordes of these insects in the spring. In other 
words, under the conditions of the season in question all the ordinary 
59405—Bull. 132—08——3 
