99 



In studying the influence of temperature on development the figures 

 upon the separate stages serve best, as they give the widest range. In 

 each stage it may be seen that the maximum time is nearly, if not 

 quite, four times the minimum, while the average effective tempera- 

 ture difference is in the inverse order, but about 2 to 1. In compar- 

 ing the minimum and maximum total effective temperatures, it appears 

 that when the average temperature is lowest the total heat required 

 to complete the development of the stage is nearly twice as great as 

 when the average temperature is highest. The length of the develop- 

 mental period is therefore not exactly inversely proportional to the 

 change in temperature. The retarding influence of decreasing tem- 

 perature appears to affect each of the immature stages in very nearly 

 the same degree. The total effective temperature required forms a 

 specific constant, which is fairly uniform for average effective tem- 

 peratures of between 30° and 40° F. These temperatures would, 

 during most seasons, prevail from June to October, inclusive. As 

 the average effective temperature falls below 25° F., however, there 

 results a great and disproportionate retardation in the development. 

 The reason for this difference may lie in the fact that when tempera- 

 ture is ascending from 32° F. it must attain a higher point to start 

 weevils into activity than that at which the same weevil will cease 

 activity when the mercury is going down. 



The observations upon the length of the entire developmental period 

 were made upon several different series of weevils. As is clearly 

 shown in the summary given in the latter part of the table, the sum 

 of the average lengths of the three stages agrees remarkably closely 

 with the length of the entire period as found in the 887 cases observed. 

 This close agreement, reached b}^ entirely different methods, indicates 

 that the series from which the averages are obtained are sufficient^ 

 large to give constant results, and therefore that the average period 

 of development throughout the season of weevil activity is very close 

 to 19 days. 



This thermal influence upon activity in feeding and oviposition ma}^ 

 be shown by taking various lots of weevils at intervals through the 

 season. For this purpose the work of 10 males and 10 females has 

 been selected, using the laboratory records for each lot. The time 

 covered is 25 days in each case to secure a fair average, and 25-day 

 intervals separate the lots from each other. The season thus covered 

 begins with June 6 and ends with November 28, 1903. To make the 

 comparison fair, average conditions as to sex, age, and individual 

 activity must be established, and the records have been selected with 

 these conditions in view. 



