THE CODLING MOTH IN MICHIGAN. 



35 



Length of pupal stage. — Owing to the very variable climatic condi- 

 tions during the pupal period there resulted a considerable difference 

 in the length of the pupal stage. The observations for the spring 

 brood extended from May 14 to July 8, during which time records 

 were taken from 122 individual insects. 



Table XXXIV. — Length of pupal stages of the spring brood; summary of Table XXXIII. 



Number 

 of obser- 

 vations. 



Pupal 

 period. 



Number 

 of obser- 

 vations. 



Pupal 

 period. 



Number 

 of obser- 

 vations. 



Pupal 

 period. 



3 

 2 

 4 

 12 



Days. 

 13 

 14 

 15 

 16 



18 

 22 

 23 

 20 



Days. 

 17 

 18 

 19 

 20 



14 

 2 

 2 



Days. 

 21 

 23 

 24 



June 



Fig. 12. — Curve of spring pupation of the codling moth in 1911, at Douglas, Mich. (Original.) 



The results are given in Table XXXIII and are further summa- 

 rized in Table XXXIV. The average length of the pupal stage was 

 18.4 days, the minimum length 13 days, and the maximum 24 days. 



Relation of temperature to the duration of the pupal stage. — From 

 general observations it has long been known that the temperature 

 has a marked effect upon the duration of the pupal stage. The 

 intimacy of this relation has already been pointed out by different 

 investigators and most recently by Prof. E. D. Sanderson in a paper 

 on the relation of temperature to the growth of insects. 1 



In our tentative effort to find the existing relation of the tempera- 

 ture to the length of the pupal period at Douglas, Mich., the average 

 temperature has been taken from the average daily temperature 



Journ. Econ. Ent., Ill, p. 113, 1910. 



