THE CODLTXG MOTH IX THE YAKIMA VALLEY 



55 



VARIATIONS IN THE SEASONAL HISTORY OF THE CODLING MOTH 

 IN THE UPPER AND LOWER YAKIMA VALLEYS. 



Owing to the fact that the Yakima Valley is divided into two large 

 sections, the upper and the lower valleys, and that the season in the 

 lower valley is somewhat earlier than in the upper, some studies were 

 made by means of banded trees and screen cages to ascertain the 

 effect this difference would have on the seasonal history of the codling 

 moth. 



In Figure 33 a comparison is made between band records secured 

 in 1919 at Yakima in the upper valley, and at Buena in the lower 

 valley (see also p. 20). The solid line is a record of the occurrence 

 of larvae under bands at Yakima, with an elevation of 1,100 feet, and 

 the dotted line records the same thing for Buena, with an elevation 

 of 850 feet, the two stations being approximately 16 miles apart. At 

 Buena the maximum number of first-brood larvae occurred July 3, 

 and at Yakima a high point was reached July 17, which, judging from 

 insectary records, probably represents the true maximum more accu- 

 rately than the high point of August 1. Thus there was an interval 



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Fig. 33.— Occurrence of codling moth larvae under bands on apple trees at two points in the 

 Yakima Valley, Wash., 1919. 



of 14 days between the two stations. For the second brood the 

 maximum at Buena occurred August 23. At Yakima the actual 

 maximum occurred September 18, 26 days later, but this was due to 

 an accumulation of larvae delayed by cold weather occurring Sep- 

 tember 8 to 13, and it is believed that the true maximum should have 

 been about September 3, or 11 days later than at Buena. 



In 1920 not enough larvae were secured at Buena to show con- 

 clusively when the maximum for the broods occurred, but the ap- 

 parent maximum at Buena occurred several days before that at 

 Yakima. 



Temperature records were kept in the orchard at Buena in 1920 and 

 1921 with a thermograph, and a comparison of these with similar 

 orchard records at Yakima shows that the average monthly tem- 

 perature at Buena is higher than that at Yakima. The average 

 difference in 1920 and 1921 for each month during which records were 

 taken has been figured and was as follows: April, 4.7°; May, 3°; June, 

 3.1°; July, 2.4°; August, 2.3°; September, 2.4°; the average for the 

 season being 3°. 



Screen cages containing from 50 to 200 larvae were also placed at 

 various points in both valleys in 1920, 1921, and 1922 and examined 



