THE SPUING GRAIN-APHIS OB ' ' GREEN BUG. ' ' 



51 



REARING METHODS. 



All of the rearing work, unless otherwise stated in the text, was 

 conducted out of doors under as nearly normal conditions as it was 

 possible for us to secure. The wheat plants on which the Toxop- 

 tera were confined were grown in flowerpots and covered with 

 lantern globes, over the top of which was drawn a very thin fabric 

 commercially known as swiss. The 

 pots were placed on a rearing stand 

 having one side hinged in such a 

 manner that it could be let down in 

 fair weather and closed up in case of 

 gales or severe beating storms. This 

 stand with its contents is illustrated 

 in Plate II, figure 1 . A thermograph 

 was placed in this stand, and thus 

 continuous records of temperature 

 were secured. 



In the middle of the summer of 

 1907 two series of investigations were 

 begun and were continued until De- 

 cember to determine the number of 

 generations. In both 1908 and 1909 

 series of generation studies were begun 

 in spring with the egg (fig. 11) and 

 continued until the egg-laying forms 

 appeared in the fall. In making these 

 observations, the first individuals to 

 hatch from the eggs in the spring 

 were isolated; the first-born from 

 these were in turn isolated, and this 

 process was continued throughout the 

 season until the egg-laying forms ap- 

 peared. The last-born was also kept 

 and the same mode of procedure con- 

 tinued until fall, as was the case in the line of the first-born. * All 

 young other than the first-born of the first series and the last-born 

 of the second series were counted each day and destroyed. In this 

 manner, each series being considered, we would arrive at the maxi- 

 mum and minimum number of generations. During these three years 

 a vast amount of data, besides that on the number of generations, 

 was thus accumulated. (See table, pp. 52-57.) 



Fig. 11.— The spring grain-aphis: Eggs as 

 deposited on leaf: a, Dorsal view; 6, lat- 

 eral view. Greatly enlarged. (Original.) 



