APPENDIX. 



401 



THE HOP PLANT-LOUSE. 



(Phorodon humuU.) 



By Pkok. ('. V. Kii-KY. 



LIFE-HISTORY. 



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

 in New York, Wisconsin, or on the Pacilie Coast, the hop plant-louse has 



substantially the same life-round. 

 The eggs are laid in the fall on dif- 

 ferent varieties and 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 

 (Fig. 1). From this egg there 

 hatches in the spring, about the 

 time when the plum buds begin to 



Fig. 1— Winter eggs of the Hop Plant-louse, burst, a Stout female plant-louse, 

 and shriveled skin of the sexual feniaie . • , 



which laid them— enlarged. known as the Stem-mother, which 



differs from the summer individuals 

 by having shorter legs and shorter honey- 

 tubes (Fig. 2). She gives birth, without the 

 intervention of the male, to living young, and 

 this method of propagation continues till the 

 last generation of the season. The second 

 generation grows to full size and gives birth 

 to a third, which becomes winged (Fig. .3), 

 and develops after the hops have made con- 

 siderable growth in the yards. The winged 

 lice then fly from the plums to the hops, de- 

 serting the plum trees entirely and settling 

 upon the leaves of the hops, where they begin 

 giving birth to another generation of wing- 

 less individuals. 



These multiply with astonishing rapidity* 

 for from five to twelve generations, carrying 

 us in point of time to the hop-picking season. 

 There then develops a generation of winged 



Fig. 2 — The Hop Plant-louse, 

 stem-mother, with enlarged 

 antenna above— enlarged. 



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

 the rate of three per day under favorable 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 of a summer, to trillions. The issue from a single stem-mother may thns, 

 under favorable conditions, blight huudreds»of acres in the course of two or three 

 months. 



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