194 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 15 



during the period of any stage of the insect would be the same for all 

 temperatures.^ 



The unit of temperature used is the day-degree. It may be de- 

 fined as a temperature of one degree acting for a period of one day. 



Table 1 gives the results of the studies on the incubation period 

 based upon observations on 4175 eggs. 



TABLE /. TEHPERATURE ANOTHE 

 INCUBATION PiRIQD OF THE COOUIVG'MOTH 



The average mean daily 

 temperatures which pre- 

 vailed during these obser- 

 vations varied from 61.6 to 

 84 deg. Fahr. and the periods 

 from 14 to 5.52 days. De- 

 velopment of the egg 

 proceeds only at tempera- 

 tures above 50 deg. Fahr. 

 The rate of development 

 increases as the temperature 

 rises above 50 deg. until 

 it reaches 88 deg. at which 

 point development is at 

 the maximum rate. The 

 third column gives the aver- 

 age daily day-degrees above 50 deg. and column 6 gives the product 

 of the day-degrees in column 3 by the periods in column 2. These 

 products are fairly uniform for the lower temperatures,- but increase 



at the higher temperatures, 

 because during the warmer 

 part of the season the tem- 

 perature for a part of the 

 time was above 88 deg. and 

 the day-degrees in column 

 3 contain some day- 

 degrees above 88 deg., 

 which retard development. 

 To make the needed 

 correction in the day- 



TABLB Z. TEnPERATURE AATOrME 

 LARVAL PERIOD OF THE eoOLINa-MOTH 



^Humidity and evaporation under out-of-door conditions have such a slight 

 effect upon the rate of development that for practical purposes they may be disre- 

 garded . 



2An exception should be noted in the case of the total day-degrees when the mean 

 daily temperatures averaged 61.6 and 63.11 degrees. The total day-degrees at these 

 temperatures are greater than at other temperatures. This indicates that possibly 

 the threshold of development is greater than 50 deg. 



