12 



) 

 Peovinciai. Board of Horticulture. 



1897 



(Fio. D.) 

 The hop plant louse, male. (Enlarged. ) 



The above are reported from Okanagan, Mission, Hazelmere, Shortreed, Kamloops Alder 

 grove, Steveston, Squamish and Saanich. 



Wherever it occurs, whether in England or on the continent of Europe, in New York, 



Wisconsin, or on the Pacific Coast, the Hop Plant Louse (Phorodon humuli) has substantially 



the same life round. The eggs are laid in the fall on different varieties and 



Hop Aphis. species of the plum, both wild and cultivated. They are small, glossy, black, 



ovoid, and are attached to the terminal twigs, especially in the more or less 



protected crevices around the buds. 



From an egg hatches in the spring, about the time when the plum buds begin to burst a 

 stout female plant louse, known as the stem-mother, which differs from the summer individuals 

 by having shorter legs and shorter honey tubes. 



She gives birth, without the intervention of the male, to living young, and this method 

 of propagation continues until the last generation of the season. The second generation ..rows 

 to full si/.e and gives birth to a third, which becomes winged, and develops after the hops have 

 made considerable growth in the yards. The winged lice then fly from the plums to the hops 

 deserting the plum tree entirely and settling upon the leaves of the hops, where they be-in 

 giving birth to another generation of wingless individuals. They multiply with astonishfnc. 

 rapidity. Each female is capable of producing on an average about one hundred young, at 

 the rate of three per day under favourable conditions. Each generation begins to breed about 

 the eighth day after birth so that the issue from a single individual runs up, in the course o 

 a summer to trillions. The issue from a smgle stem-mother may thus, under favourable circum- 

 stances, bhght hundreds of acres m the course of two or three months. From five to twelve 

 generations are produced in the course of the summer, carrying us in point of time to the hop 

 picking season. There then develops a generation of winged females (.e.«^a.c«), which fl^y 

 back to the plum tree and give birth to the true sexual females, which never acquire win's and 

 never leave the plum tree. By the time this generation has matured, which\equi7os "but a 

 few days, varying according to the temperature, belated winged indi;iduals, which are the 

 rue males fly in from the hop fields. These fertilize the wingless true female upon the plum 

 leaves, and these soon thereafter lay the winter eggs. Thus there is but one generation^ 

 sexed individuals produced, and this at the close of the life round-the female! wSelon 

 plum-trees; the males winged on hops. All intervening generations are composelor v g°n 

 females only (parthenagenetic). This is the invariable round of the insect's life ^ 



