78 BULLETIN 1476, U. S. DEPARTMENT OF AGRICULTURE 
The data given are only preliminary, since all of the experimental 
results have not as yet been carefully checked. 
Although in the past the effect of humidity upon the development 
of an insect whose life habits prevent it from directly experiencing 
continued atmospheric humidity, has been somewhat discounted, 
it has been found that, in some manner, humidity does play an im- 
portant role in the development of the corn borer. How the ex- 
ternal humidity affects the borer within the stalk can, of course, 
only be conjectured; but the fact that it does affect it serves to illus- 
trate the fallacy of attempting to derive a close correlation between 
development and a single factor of climate, which will apply and 
prove useful over a period of years. 
In the investigations thus far the importance of fluctuation of 
temperature in lengthening or shortening a stage has been very 
marked, and in many instances where the temperature has been 
higher, humidity conditions the same, but fluctuation less, there has 
been a marked increase in the period required to complete a given 
stage. 
The entire difference in duration of stages apparently produced 
by fluctuation is not due to the mere rise and fall of temperature. 
A study of recent constant temperature experiments shows that the 
lower temperatures, i. e., 10° or 15° above the actual threshold of 
development, have a much greater effect upon development than 
those temperatures 20° or 30° higher. Since during the spring 
months the daily temperatures are for a greater part of the time 
within these more influential limits, an accurate evaluation of the 
effects of these temperatures must be considered before any definite 
knowledge can be obtained concerning the possibilities of develop- 
ment at this time of year. 
However, variation in temperature is more advantageous to de- 
velopment than is constant temperature, although the advantage 
seldom rises over 10 per cent in favor of the former, and in most 
cases can be figured at 2 or 3 per cent. 
The results of the experiments in connection with this type of 
investigation will be advanced far enough in the near future to 
warrant a more detailed discussion of these physiological reactions. 
Although it is not expected that a definite mathematical interpreta- 
tion can be evolved that will express the effects of climate in relation 
to development, it is hoped that certain definite facts may be learned 
which will give a much clearer appreciation of the possible reactions 
of the insect to its environment. 
Precipitation, as a determinant of development in entomological 
research, has not, until very recently, been given the attention which, 
upon closer scrutiny, it seems to merit. That the distribution of 
precipitation during the winter and spring months is of immense 
importance biologically can not be denied, but in just what par- 
ticular manner this factor affects the future seasonal activities of 
this insect can not at present be explained. 
During the last three years a preponderance of precipitation in 
March, April, and May, followed by a dry June, induced an early 
start of the insect in New England, and so far under these condi- 
tions a complete second generation has occurred and evidences of 
a partial third generation were observed. On the other hand a 
deficiency of rain in March, April, and May, followed by a rainy 
