Octobpr, '11[ CUSHMAN: BIOLOGY OF BOLL WEEVIL 443 



in this manner, the total period varied from eleven to nineteen days. 

 The former is probably a somewhat shorter time than actually elapsed 

 in any case, but the error was counterbalanced by the later weevils 

 in the same lot of squares. In all probabiUty, the earhest weevils from 

 a, lot of eggs deposited within twenty-four hours came from the earliest 

 eggs and the latest from the latest eggs, so that, other things being 

 equal, the developmental period of all the weevils from these eggs would 

 be equal. 



One of the principal factors in causing variation in the length of the 

 developmental period within a given lot of squares and between 

 different lots of squares during the progress of the work was the con- 

 dition of the food supply. This factor was most troublesome and 

 most difficult of control, especially in small lots of squares and late 

 in the season. 



The following table shows the variation in the length of the develop- 

 mental period and the number of weevils requiring the different 

 periods for development: 



TABLE VII 



Another factor which largely affected the development of the wee- 

 vils was the temperature. In order to indicate as nearly as possible 

 the elTect of temperature on the length of the developmental period, 

 the weighted average daily and periodic developmental periods were 

 calculated for all of the weevils bred. The average daily period 

 varied in duration from twelve to nineteen days, but, as each of these 

 extremes include data on only one weevil each, the variation is more 

 accurately shown by the thirty-three weevils emerged on August 7, 

 which averaged 12.45 days, and the twenty emerged September 22 

 which averaged 16.67 days. The average period for the 868 weevils 

 reared was 13.68 days. 



For convenience in showing the effect of the temperature on the dura- 

 tion of the developmental period, the dates of emergence were divided 

 as far as possible, into groups of ten days each and the weighted average 



