PE0GEESS EEPOET OX THE EUROPEAN CORN BOEEE 79 
June, were unfavorable, and in those years in which such conditions 
have prevailed there has been a diminution in the number of indi- 
viduals developing a second generation. 
In order to present a picture of conditions in several representa- 
tive localities where P. nubilalis is known to exist, a series of climo- 
graphs for these localities have been constructed, following the 
methods Of Taylor (66) and Shelf ord (57). These are shown in 
Figures 39 and 40. All data used in the construction of these 
climographs have been based upon normal means, and the graphs 
may be taken as representing mean conditions of typical localities 
in the areas indicated. Temperatures are plotted along the " Y " 
axis and tenths inches of precipitation along the " X " axis. The 
numerals along the lines composing the graphs refer to the months 
of the year. The 3-inch precipitation line has been made a heavy 
broken line to give an easier means of comparison and differentia- 
tion between the months. It must be understood that these graphs 
will not indicate definite conclusions; they serve rather to show 
the differences in climate existing in normal years. The comparative 
deficiency of precipitation which exists in the one-generation areas 
can be readily appreciated by a comparison of Figure 39, C and D, 
with Figure 39, B, which represents a two-generation area. In view 
of the uniform advantage of temperature which Hungary, repre- 
sented by Figure 39, C, has over New England (fig. 40, A), the 
deficiency of precipitation in Hungary would lead one to believe 
that here was a potent factor in limiting the number of generations 
annually to one, whereas the New England climate (temperature and 
precipitation) has been favorable for two generations. Compare 
the localities in the United States known to be infested by P. 
nubilalis; New England (fig 40, A) with eastern and western New 
York (fig. 40, B and C) and Ohio (fig. 40, D). Note the difference 
in the distribution of precipitation, particularly during the winter 
and early spring. Again the deficiency and distribution of precipi- 
tation appear to separate New England's two-generation area from 
the New York and Ohio one-generation conditions. 
The graphs for the Corn Belt (fig. 39, A) have been inserted as a 
means of visualizing the normal conditions which exist in the 10 
towns selected in comparison with the localities from which seasonal 
history information has been obtained. Note the dotted graph of 
Sioux City. Again, the comparative deficiency of precipitation dur- 
ing the critical winter and early spring months would lead one to 
believe that there would be a strong possibility of only one genera- 
tion in that section of the United States. 
The accompanying graphs representing the one and two genera- 
tion localities are typical of similar graphs constructed for 111 
single-generation and 52 two-generation localities in Europe, Asia 
Minor, and the United States, where P. nubilalis exists and from 
which seasonal-history data are available. It must be borne in 
mind, however, that such comparisons are certainly not proof of 
what might happen in similar areas not now infested, although useful 
in studying locality conditions and in formulating various hyphoth- 
eses which must be tested experimentally. Prognostications 
founded upon empirical comparisons of this nature are extremely 
dangerous and should be used only as a key to avenues of experi- 
mentation. 
