THE KANSAS UNIVERSITY 



SCIENCE BULLETIN 



Vol. XIV.] October, 1922. [No. 10. 



A Problem in the Relation of Temperature to 

 Rate of Insect Development. 



By p. A. GLENN, 



Chief Inspector, Division of Plant Industry, Illinois State Department of 

 Agriculture, Urbana, 111. 



EVEN the most casual observer is familiar with the fact that low 

 temperatures inhibit growth in plants and animals, that hiber- 

 nation or death will be evidenced by temperatures approaching 

 freezing, and that high temperatures favor rapid development. It 

 is only in late years that biologists have attempted to ascertain 

 with accuracy the reaction of various plants and animals to differ- 

 ent degrees of heat. It has now been quite definitely demonstrated 

 that development will take place only when the temperature is 

 above a certain point, called the zero of development, or the 

 threshold of development; that within a certain range of tempera- 

 tures above this point the increase in the rate of development is 

 approximately proportional to the rise in temperature; and that 

 under given conditions of high moisture, evaporation and other 

 physical environmental factors aside from heat, there is a tempera- 

 ture constant for each period in development, which is equal to the 

 product of the period by the average temperature above the thres- 

 hold of development. 



This range of temperatures within which the rate of development 

 increases as the temperature rises is bounded at the lower end by 

 the threshold of development, and at the upper end by what I 

 shall call the degree of the maximum rate of development. It is 

 found that at temperatures near the lower limit of this range the 

 rate of development varies somewhat faster than the rate of change 

 in temperature, and at temperatures near the upper limit the rate 

 of development varies somewhat more slowly than the rate of change 



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