A NEW INTERPRETATION OF THE RELATIONSHIPS OF 
TEMPERATURE AND HUMIDITY TO INSECT DEVEL¬ 
OPMENT 
By W. Dwight Pierce, 
Entomological Assistant , Southern Field Crop Insect Investigations, Bureau of 
Entomology 
INTRODUCTION 
Upon the proper interpretation of the laws of climatic control of life 
rests the solution of many practical problems, and inasmuch as all 
plant and animal life reacts to climate in the same general manner it is 
apparent that the study of the climatic control of insect development 
may throw light upon the problems of all other forms of life. It has 
been apparent to some workers in the field of ecology that our so-called 
laws of effective temperature were deficient in many respects. A large 
number of phenomena were not properly explained by any known theory. 
It is with the hope that the present interpretation may come closer to 
the truth that this paper has been prepared. 
Biologists for years were laboring with the theory of a fixed zero of 
effective temperature for all life, and only recently was it accepted that 
each species might have a different zero. It has been the custom to 
determine the thermal constant for any given activity by multiplying 
the number of effective degrees accumulated above the effective zero in 
daily units of mean temperature by the time in which the given phe¬ 
nomenon took place. The noneffective low temperatures were elimi¬ 
nated, but not the time in which they were experienced. Inasmuch as 
most workers were located in north-temperate climates, where high 
noneffective temperatures seldom occur, it had not occurred to them 
that some high temperatures might not be effective and that there was 
another boundary to the effective zone besides the zero. These high 
temperatures and the time in which they are experienced must be elim¬ 
inated. In addition to all of these errors in method, there has been no 
correlation of the humidity factor until very recently, although now 
many workers are trying to solve the part played by this factor. 
The principal data upon which the writer has based his studies in¬ 
clude records of thousands of individual boll weevils (Anthonomus grandis 
Boh. and A . g. thurberiae Pierce), made by the members of the boll-weevil 
force under the direction of Mr. W. D. Hunter and the writer at various 
localities in Texas, Louisiana, and Arizona throughout the period of 
years from 1902 to 1915. At each place where biological notes were 
made a thermograph-hygrograph record was kept, and this record was 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
dc 
(1183) 
Vol. V, No. as 
Mar. 20, 1916 
K—27 
