APHIDES. 181 



In 1887, Prof. Riley (Entomologist of the Depart- 

 ment of Agriculture of the United States) set the 

 matter of migration from Plum, to Hop, beyond doubt 

 by his observations, of which a part was read before 

 our own British Association ; he mentioned : — 

 *' Phorodon humuli hybernates in the winter egg state, 

 this egg being fastened to the twigs (generally the 

 previous year's growth) of different varieties and 

 species of Pninus, both wild and cultivated." From 

 the winter egg Prof. Piiley found the female, the 

 mother of the coming tribe to be hatched, the winged 

 descendants of which female take flight to the Plum. 



The existence of many generations on the Hop, 

 during summer, we are all well acquainted with ; but 

 during Prof. Piiley's stay in Europe, and more especi- 

 ally in England, he personally observed the point not 

 previously worked out, of the autumn migration of 

 the Hop Aphis, back from Hop to Plum, in the close of 

 uutumn. 



These observations, coming from such a high 

 authority as Prof. Riley, give thorough confirmation 

 to the belief previously held as to migration ; but still 

 I do not think that in this country the whole of the 

 attack comes on the wing from Plum, Damson, or 

 Sloe, because (amongst other reasons) we have found 

 Aphides— that is, wingless females and lice — on Hop 

 as early as the end of March and the beginning of 

 April, long before the attack coming on the wing 

 made its appearance. 



The Hop Aphides (the Phorodon or Aphis humuli) 

 may be distinguished from the Plum Aphis, and from 

 others of the Aphidince, by the horns being hardly 

 longer than the body, together with the lowest joint 

 being toothed or gibbous, and the tubercles on the 

 forehead each having a strong tooth. The legs are 

 short, and the honey-tubes long. 



Where there chance to be large quantities of Sloes, 

 as, for instance, Sloe hedges, in the neighbourhood of 

 Hop-gardens, these at least might be got rid of with- 

 out loss. 



