78 



The Hop Aphis. 



the insects coat the leaves below and give them a dark, shiny 

 appearance. Finally, this " honey dew " turns black, the grow- 

 ing shoots shrivel and curl, and the development of the whole 

 plant ceases. Sometimes after such a " black blight " the plant 

 clears itself later in the season, and should heavy, rain wash the 

 leaves, it will put forth a little new growth on which a few hops 

 will be carried. Should the conditions be less favourable for the 

 rapid multiplication of the aphis, lice may be found on the plant 

 during the whole season and will then harbour in the cones of 

 the hops ; as they die there the remains turn black owing to the 

 invasion of a fungus, and the hops, after picking and drying, 

 will be found with black cores, by which their value is much 

 deteriorated. 



Description and Life History. 



The Hop Aphis belongs to the large family of plant lice, 

 which includes many of the most characteristic pests of the farm 

 and garden, such as the well-known ' : green fly " of the rose, the 

 black " collier " which infests the tops of broad beans, the black 

 cherry louse, the lice of apples, plums, and currants, the aphis of 

 corn and of the turnip, &c. 



The mature form of the Hop Aphis is about one-eighth inch 

 long, with a plump body and three pairs of legs ; the mouth is 

 prolonged into a proboscis adapted for piercing the leaves of the 

 plant and sucking the sap upon which the insects live ; towards 

 the extremity of the abdomen are two tubes from which exude 

 the sticky " honey dew." Two pairs of transparent wings may or 

 may not be present ; for both winged and wingless female forms 

 occur, the former being generally distinguished as "fly" from 

 the wingless " lice " ; there is also a winged male. 



Two cycles of life history are known ; one complete on the 

 hop, the other involving a migration from the sloe, damson or 

 plum back to the hop again. 



In the first cycle the wingless female form hibernates in the 

 ground and crawls on to the hop plant in the spring, when she 

 immediately begins to deposit living young upon the soft leaves. 

 These young in their turn begin to reproduce themselves with- 

 out the intenention of a male for many generations, multiplying 

 with astonishing rapidity. Some of these lice enter the pupal 

 state, from which they emerge as winged females and fly to 



