LIFE HISTORY. 



11 



was unable to find this condition, but the foregoing data show the 

 possibility of another method of hibernation. 



Many examinations of hop roots were made during this investiga- 

 tion, but no eggs of the hop aphis were discovered on or near them. 

 The following data, however, lead the writer to believe that the 

 aphides very frequently hibernate on or around the hop roots. 



Wingless viviparous hop aphides were observed depositing young 

 upon the lower leaves of a hopvine at Santa Rosa, Cal., March 16, 

 1912. This vine was half a mile from any prune tree. Many small 

 wingless aphides were observed on the lower leaves of hopvines at 



Fig. 1.— Field cages so placed as to catch any hop aphides that might emerge from eggs deposited upon 



the hop roots. (Original.) 



Perkins, May 16, 1912o No winged migrants were observed at this 

 time. 



The first winged migrants were observed at Perkins on May 24, 

 both on the prune and the hop, and in the latter case were only on 

 the upper leaves, the lower leaves being entirely free. 



Although field cages (fig. 1) which were placed over hopvines in 

 February and removed after the surrounding vines were thoroughly 

 infested did not contain any hop aphides, the fact that aphides were 

 present on the hops before the winged migrants appeared and that 

 they were found upon the lower leaves, while the winged forms 



