410 



remaining 118 larvae (divided into 18 lots) were grouped as follows: 



July 22d to 28th 18 larvae 17% failure to pupate. 



July 31 to August 3d, 37 larvae 38% failure to pupate. 



August 7 to 8th 28 larvae 89% failure to pupate. 



During the period July 22d to August 8th there had been no niininiuni 

 outdoor teni]ieralures below 57''F. ; all larvae collected in that period, 

 therefore, were experimentally subjected to temperatures below o()°, in 

 order to make them comparable with larvae collected on August 9th and 

 10th, when outdoor temperature in the early morning fell to 53° F. The 

 lots collected August 9th to August 14th (35°) showed 88 per cent failure 

 to pupate. These experiments showed no indication of cool night effects 

 but rather indicated a seasonal increase in the number of individuals fail- 

 ing to pupate, beginning about August 1st, regardless of minimum 

 temperatures. 



The effect of summer and autumn rainfall on the length of time to 

 pupation of hibernating larvae is suggested by the following data: 

 Case a: One hundred and eight larvae collected August 20th to September 

 12th, 1919 (kept at a temperature of 70° and humidity of 40 per cent 

 until August 30th if collected before that date), were subjected to tem- 

 perature near 32° F. and humidity of approximately 100 per cent until 

 January, when they were placed in conditions favorable to pupation. 

 Between January 26th and February 24th, only 5 larvae, or approximately 

 3 per cent pupated. The average time to pupation was 19.3 days at 83° F. 

 and 21.5 clays at 63.5°. Case b: Larvae collected October 20th of the 

 same year (1919) were treated exactly the same as those in Case a, and 

 60 per cent of them pupated, the length of the prepupal stage being as 

 little as 11 days and averaging 17.8 days at 83° F. The pupal life was 

 about 10 per cent shorter than in the case of the sets collected earlier. The 

 differences between those collected on or before September 12th and those 

 collected on October 20th were thus very striking, both in the per cent 

 pupating and in the time to pu]3ation, when the larvae were placed under 

 favorable conditions. The differences lie in the time of emergence from 

 the apple, and in the weather conditions between September 12th and 

 October 20, 1919. There was very little rain during the period of collec- 

 tion in August and the first twelve days of September, but during the 

 latter part of September and the iirst 20 days of October there were 5 

 rainy periods and great variations in temperature (26° to 96°). These 

 observations do not show whether it was the condition of food, tempera- 

 ture, moisture, or variability which produced the result. They serve, 

 however, to indicate the necessity for year-round experimentation. 



The calculation of velocity values for larvae which had passed the 

 winter under known conditions afforded unusual difficulties because their 

 pupation showed essentially the same seasonal curve as the emergence of 

 moths (Fig. 25). Larvae kept in the laboratory at temperatures of 40°- 



