THE CODLING MOTH IN THE YAKIMA VALLEY. 59 



After December 15, the weather gradually became warmer, and 

 for a number of days the temperature remained above the freezing 

 point. 



All the wintering larvae in the insectary succumbed to this extreme 

 cold. Examinations of larvae wintering on apple trees were made 

 in various localities during the succeeding two months in order to 

 ascertain the effect of different degrees of freezing on the larvae. 

 It was found that where minimum temperatures of — 15° to — 20° F. 

 had been experienced from 70 to 80 per cent of the larvae were killed. 

 Minimum temperatures of —20° to —25° F. had killed from 80 to 

 90 per cent of the larvae, and minimum temperatures of —25° F. 

 and lower had killed all the larvae. In all cases the larvae examined 

 had no other protection than bark or burlap bands. Larvae occurring 

 below the snow line of December 13 or in the soil all survived, no 

 frozen individuals being found in these places. These protected 

 individuals made possible the continuance of the codling moth in 

 the colder localities. 



On January 18 and 19, 1922, the minimum temperature at Yakima 

 was — 4° and —8° F., respectively, and on several other days in 

 January the minimum was zero. An examination of wintering 

 larvae on the trunks of apple trees near Yakima was made April 17. 

 Of 346 larvae examined, 15, or 4.3 per cent, had been frozen. 



WINTERING PERIOD. 



During the season of 1920, records were kept of the date of leaving 

 fruit of all wintering larvae, and in the spring of 1921 the dates of 

 pupation of these larvae were recorded. These figures show a wide 

 variation in the length of this period. One lot of 176 larvae collected 

 under bands on September 18, 1920, which had all probably left the 

 fruit within a period of three or four days, pupated over a period of 

 58 days in the spring of 1921, or from April 10 to June 6, inclusive, 

 as shown in Table 45. The pupal period was more than usually 

 prolonged in 1921, however, owing to fluctuations of temperature. 

 A cold wave in the middle of the pupation period, from April 21 to 

 May 4, delayed the pupation of many larvae and resulted in two 

 maximum periods of pupation instead of the usual one (see Fig. 23) . 

 On the other hand, there is a definite tendency of the earlier-matur- 

 ing larva? to pupate earlier than those maturing later in the fall. 

 The pupation of 49 wintering first-brood larvae was recorded, and of 

 these 35, or 71 per cent, pupated during the first half of the pupation 

 period, that is, April 9 to May 5, inclusive. Records were obtained 

 of 499 wintering individuals of the second brood, exclusive of the 

 ot of 176 mentioned above. As shown in Table 46, approximately 

 lalf of the larvae leaving the fruit in August pupated before May 5. 

 3f those maturing in September, about two-thirds pupated before 

 VTay 5, while of those maturing in October, only one-third pupated 

 before May 5. 



