116 



THE HOP. 



not have to contend against the hop plant louse, but 

 about i888or 1889 the insect made its appearance there, 

 spread with the astonishing rapidity characteristic of 

 plant lice, and, in 1890, accomplished the damage 

 which we have noted in a previous paragraph. 



The life history of this important insect has been 

 fairly well understood in Europe for many years. It is 

 remarkable from the fact it possesses a dual food-habit, 

 living through the summer only upon the hop plant 

 and passing the autumn, winter and early spring upon 

 the plum. It is the first species of plant lice of which 



FIG. 56. HOP PLANT LOUSE. FIG. 57. HOP PLANT LOUSE. 



True female. Stem mother. 



Greatly enlarged. (From Insect L\fe.) 



this peculiarity in life history was definitely proven, 

 although it has since been shown to be common 

 enough among species found in the summer time upon 

 annual plants. It is strange that the discovery of this 

 mode of life was not made earlier, since the necessity 

 should have been obvious enough to anyone who 

 might think about it. The necessity for this migration, 

 however, is even more marked with the hop louse than 

 with species feeding upon other annual plants, since 

 not only does the hop vine die down in the fall, but 



