Insects., etc., Injurious to the Damson. 



249 



three generations, but there may be only two, or as many as five, 

 depending upon the food. 



The damson form assumes wings, and then leaves the first plant 

 host and betakes itself to the hops. This migrating form is a 

 winged viviparous female with small cephalic and antennal processes. 

 They appear on the hops from May onwards. In 1897 the migration 

 lasted from the 25th of May to the 14th of June a "climatic check" 

 came in between. In 1899 they did not leave the damson until the 

 20th of June. From the few observations I have made, I find even 

 approximate dates difficult to give. 

 All that we can definitely say is 

 that somewhere about the end of 

 May to the second week in June 

 the aphides leave the damsons, 

 sloes, and other prunes, and fly 

 off to the hops. These winged 

 migratory forms are viviparous 

 females, which at once commence 

 to bring forth living young, the 

 so-called lice. Within ten days 

 of birth these lice become the 

 apterous viviparous females, and 

 produce other lice, and so on for 

 several generations. These lice 

 and apterous females have not 

 only more distinct frontal tuber- 

 cles, but also a distinct process on 

 each basal joint of the antennse. 

 Sometimes these viviparous wing- 

 less females or lice may turn 

 into pupse, and so another brood 

 of winged females in the summer, 



which fly from hop bine to bine and garden to garden. This, I 

 noticed in 1897, took place on a number of bines where lice were 

 in great abundance early in August. These wingless and sometimes 

 winged viviparous females go on until the autumn, when they nearly 

 all enter the pupal stage, become winged, and leave the hops. The 

 dates of this migration vary. In 1896 I noticed them moving 

 on the 20th of September, and again on the 22nd. In 1899, the 

 first migration in the neighbourhood of Ashford took place on the 

 18th of September, when the air was laden with them ; another 

 large migration took place on the 28th of the same month ; whilst 



[ir. //. Hammond. 



FIG. 181. OVA OP THE HOP-DAMSON APHIS 

 (Pkorodoii humiili). 

 (Slightly enlarged.) 



