THE HESSIAN FLY. 11 
posed distasteful variety is in a condition more satisfactory to the 
insect at the time of oviposition. It is doubtful, however, if this can 
be said of the attack of the second brood on the more matured plants, 
as it is quite noticeable that the ranker-growing varieties with strong, 
stiff straw are the least affected. Then, too, among fall wheats in the 
northern part of the country it is quite essential that a wheat plant 
be able to send out tillers from the old roots of plants killed by the fly 
(fig. 10), and that these tillers prove hardy enough to withstand the 
winter. Therefore, in selecting varieties of wheat with a view to evad- 
ing Hessian-fly attack, the farmer will do well to ignore statements on 
this point from those who have seed to sell and select from the varie- 
ties known to do well in his locality such as are of strong, vigorous 
growth, hardy, and with a stiff straw. 
For some reason the durum wheats do not seem to attract the fly, 
at least not the second brood. In going over fields of this kind of 
wheat in sections where other spring wheats were suffering from 
attack by this pest, 1 was rarely found on a stem of durum wheat, | 
while any straws of other varieties growing from seed that had become 
intermixed were almost invariably infested. Whether this will hold 
good in case of the young plants it is as yet impossible to say, because 
of the difficulty of telling to what varieties the young plants belong. 
Infested plants have been found in fields of young durum wheat in 
some considerable numbers; but these plants may have been of 
other varieties, as the fields had been used for other varieties the 
year belore, and besides the seed itself may have been impure. 
METEOROLOGICAL EFFECTS. 
All who have carefully studied the Hessian fly under various field 
conditions during a series of years have noted that weather conditions 
have an important influence on the msect. Especially is this true in 
its economic relations to the grains it attacks; hence in the applica- 
tion of preventive measures these weather conditions become of vital 
importance. 
Many farmers place much stress on the effect of cold weather or 
even of frosts in terminating the flies’ work in the fall, and it is for 
this reason that many try to delay wheat sowing until after there has 
been a sharp frost. The facts are that the females will be abroad and 
ovipositing in freezing weather, and Mr. W. J. Phillips has found 
by experimentation that the eggs will remain in a temperature of 36° 
F. for seventy-two hours with no other effect than to delay their 
hatching that much longer. This is about the temperature at which 
frosts would occur. Indeed, the writer has observed eggs hatching 
during the day in the fields when there were frosts nearly every night. 
Whether or not the larve from these would get sufficiently advanced 
