38 



BULLETIN 1235, U. S. DEPARTMENT OP AGRICULTURE. 



WINTERING LARVAE. 



For the studies of 1921, reared larvae of the first and second gener- 

 ations of 1920 were used, as well as a considerable number of larvae 

 collected from banded trees in September, 1920. A special study 

 of the wintering period was made, and the results are given on 

 page 59. 



PUP^E OF THE SPRING BROOD. 



Time of pupation. — The time of pupation of 732 wintering larvae 

 is shown in Figure 23. An unusually cold period, with daily mean 

 temperatures below 50° F. extending from April 22 to May 3 (April 

 28 excepted) , followed by warmer weather, caused an abundance of 

 larvae to pupate at two widely separated periods. The first maximum 



Fig. 23.— Pupation of the spring brood of the codling moth at Yakima, Wash., 1921. 



was reached on April 17 and the second maximum on May 14. The 

 first pupa was observed on April 9 and the last on June 6, giving a 

 range of 59 days. 



Length of the pupal stage. — Although 229 of the 553 pupae recorded 

 in Table 33 pupated before April 22, with a minimum average pupal 

 period of 36 days, the extremely high temperatures in the latter 

 part of May and early June so shortened the pupal period of the 

 remaining individuals that the average for all pupae was 29.53 days. 

 This is the lowest average pupal period for the spring brood that has 

 been recorded in these studies at Yakima. 



