92 THE SPRING GRAIN-APHIS OR " GREEN BUG. 



Of the five individuals involved in Table XI the two last hatched 

 from the egg March 24, the other three on March 27. This table 

 indicates the influence of high temperatures on reproduction, but 

 also shows that these affect the individual female to varying degrees. 

 The totals for the life of individual females show that all of these 

 were in the vigor of life, not having reached the decline at the time 

 the observations were made. 



These tabulations are taken from records of regular rearing and 

 reproduction investigations, and were selected wherever there 

 occurred a number of consecutive days with temperatures varying 

 both above and below freezing during each 24 hours. 



By referring to the continuous rearing by the junior author it 

 will be observed that with favorable conditions a female Toxoptera 

 will produce young every day during the most vigorous portion of 

 her life, the exceptions being toward the close thereof. 



It would probably be well to mention in this connection some 

 observations of the junior author in regard to the amount of cold 

 that can be endured by Toxoptera. 



On November 13, 1908, several viviparous females that had been 

 producing young were frozen solidly in a block of ice. They were 

 thawed out after 8 and 24 hours, respectively, and all died. These 

 may have been somewhat weakened by age, however, so on the 14th 

 2 oviparous females. 1 winged viviparous female, 1 adult viviparous, 

 and 2 individuals that had cast the third molt were frozen in a block 

 of ice and allowed to remain so for 24 hours. About an hour after 

 being thawed out, at a temperature of about 45° F., 1 oviparous 

 female and the winged female turned dark and died, the others keep- 

 ing color, but showing little signs of life. About 3 hours after 

 there were signs of life among the remaining ones; 7 hours after 

 thawing out they were still feeble: 24 hours after thawing out the 

 temperature was raised to 60° F and 1 molted. On the third day 

 after being thawed out there were 2 young in the cage. Six days 

 later all were dead except the one that was giving birth to young, 

 and her progeny. Tins will give some idea of the tenacious grip 

 Toxoptera has on life. 



Attention may properly be called to the fact that unless the utmost 

 caution is employed in the examination of plants for newly-born 

 3'oung there is great likelihood that some of them may be overlooked. 

 Thus they may be born one day under a high temperature but remain 

 undiscovered until later, when the temperature is much lower, and of 

 course be credited to the later date. In the light of all of the observa- 

 tions made by those engaged in these investigations, the minimum 

 temperature under which reproduction begins is about 40° F. Pos- 

 sibly reproduction may occur under some obscure favorable circum- 



