PROGRESS REPORT OX THE EUROPEAN CORN BORER 
77 
are sufficient to warrant doing so. in an attempt to evaluate the 
temperature influence upon seasonal development. As is noted fur- 
ther on in the discussion, the other factors are being carefully 
studied, but until experimental proof becomes stronger, it would 
be unwise to draw definite conclusions from the available data re- 
garding the future behavior of the insect under widely different 
climatic conditions. 
In nearly all investigations of important economic pests the neces- 
sity has arisen of attempting correlations with one or more climatic 
factors to aid in forecasting the time of appearance and duration 
of important phehological events. The most common correlation 
to be found is that involving the effects of accumulated degrees of 
temperature, above a threshold of development, with the seasonal- 
history features. It has been determined by experimentation that 
the methods of correlation commonly used to express the temperature 
effects upon development are not satisfactory for practical purposes, 
and until a more basic knowledge is obtained concerning the reac- 
tions of the insect to its environment, the usual temperature sum- 
mations will be avoided. 
All the climatic factors, not temperature alone, must be studied to 
obtain the*solution of these physiological problems. 
Experimental work carried on at Arlington, Mass., to date has re- 
vealed the following points: 
1. Moisture conditions, i. e., precipitation, humidity, and evapora- 
tion, have an apparent effect upon development, and in the case of 
humidity and precipitation, an effect that can not safely be averaged 
out. 
1. Individuals in New England which experienced the usual winter tem- 
peratures but were deprived of moisture up until time for normal spring 
pupation in the field were delayed in their seasonal occurrence beyond the 
normal time, and as a result of this treatment only 60 per cent of the progeny 
produced the normal two generations. 
2. Individuals which experienced a mean temperature of approximately 75° 
F. and an average humidity of less than 45 per cent during the hibernation 
period failed to pupate and died in large numbers. A small percentage com- 
pleted development under these conditions. Individuals having a similar history, 
placed under field conditions at the time for normal pupation in the field, 
were greatly delayed in their development, and the progeny completed their 
development — 60 per cent one generation, and 40 per cent two generations. 
3. Preliminary correlation work shows that humidity deficiency raises the 
threshold of development and decreases the point of maximum rate of 
development. 
2. Temperature (humidity conditions approximately 75 to 85 per 
cent) : 
Egg 
Larva 
Pupa 
1. The reciprocal of the curve of development is not a straight line, ex- 
cept within certain limits, which are 
o F 
67-87. 5 
92 
70-75 
58.7 
44.3 
o p 
61-81 
94.5 
70-75 
49.7 
36.5 
o p 
62. 5-87 
2. The maximum rate of development occurs at 
92 
3. The optimum for development (fastest rate with least mortality) is 
4. Straight -line threshold, as used bv other workers, is .. _. 
82-86 
55.4 
5. Actual threshold of development is ... 
41.2 
6. Corrections must be made for the different velocities of development 
which exist outside of the straight-line limits. 
7. The points as here given will vary in accordance with the humidity 
fluctuations or change in any of the other climatic factors. 
