6 FARMERS’ BULLETIN 640. 
occurring at this time may unite, and another supplementary genera- 
tion, as it has been termed, may be produced. The economic signifi- 
cance of this so-called generation depends much on the weather, as, 
if winter sets in before the larve have sufficiently matured to with- 
stand its rigors, these must necessarily perish, while if the mild. 
autumn weather is greatly prolonged, a greater or less number of 
them may winter over uninjured. 
LIFE HISTORY IN SPRING-WHEAT REGIONS OF THE NORTHWEST. 
The statements here made regarding the life history of the Hessian 
fly in the spring-wheat regions of the Northwest are based largely 
on the careful investigations carried out by Mr. George I. Reeves, a 
special field agent of the Bureau of Entomology, during the season 
of 1905. This single season may have been an exceptional one, in 
that the spring was backward, the summer wet, and the mild autumn 
weather continued later than usual. The results must not, there- 
fore, be taken as wholly conclusive. 
In North Dakota the insect winters in the flaxseed stage in both 
stubble and volunteer wheat, chiefiy the former. Egg laying begins 
late in May, and during seasons with plenty of rain the second genera- _ 
tion follows the first in quick succession, being reenforced by the con- 
tinued emergence of flies from stubble of the previous year. Here 
the summer conditions are different from those in the East and South, 
and the breeding season extends from about May 20 to October 1, or 
throughout the entire summer. In other respects the habits of the 
insect do not seem to differ from what they are in the fall-wheat- 
growing sections of the country. 
DISTRIBUTION. 
Outside of America the Hessian fly occurs in North Africa, western 
Asia, Europe, British Islands, and New Zealand. In the Dominion 
of Canada Fletcher found it from Prince Edward Island to Indian 
Head, Saskatchewan. On the Pacific coast it probably occurs from 
central California to British Columbia; but as no exact investigations 
have been made there, this statement is to be considered as only 
approximately correct. 
Our previous notions of the distribution of this insect over the 
country east of the Rocky Mountains will have to be revised. The 
accompanying map (fig. 8) shows the extent to which this revision 
becomes necessary. 
The dotted area indicates the present distribution of the Hessian 
fly based on our latest observations and data furnished by Prof. 
Lawrence Bruner, of Nebraska, and Mr. R. I. Smith, entomologist of 
the Georgia State crop pest commission. This is believed to be 
approximately correct. It also seems to show that the insect must 
