HOP APHIS. 1^1 



ful examination of specimens of Aphides both from Hop and 

 Plum, and reports from Hop-growers (noted at length with 

 figm'es in my Eeport for that year), I mentioned that there 

 appeared to me to be reason to beheve that the great attack, 

 which usually occurs in the form of "Fly" about the end of 

 May, comes on the wing from Damson and Sloe, as well as 

 (which at this present date of writing I still think is to some 

 extent the case) from Hop. 



In 1887, Prof. Riley 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 liumidi 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 Pnuuis, both wild 

 and cultivated." From the winter egg Prof. Pdley 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. 

 Riley's stay in Europe, and more especially 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 autumn. 



On September 15th Prof. Riley wrote me from Maidstone, — 

 " As I anticipated, I have found Phorodon humidi just migrat- 

 ing from Hop to Prune, and first wingless generation on 

 Prune, but no eggs yet." 



On September 24th also, writing from the neighbourhood 

 of Maidstone, Prof. Riley noted, "Phorodon swarming on 

 Plum-trees here." 



On October 1st Prof. Riley wrote me that he had now 

 brought the Phorodon investigations to a successful close, and 

 completed the whole life-cycle. "Last week pairing was 

 everywhere going on, and on Saturday I noticed the first 

 eggs. The Plum-trees are now being rapidly stocked. The 

 male is winged and the female wingless, as I had surmised, 

 and the first generation on the Plum is the sexed one." 



Further, Prof. Riley informed me that the Aphis eggs 

 (which he had seen on the Plum-shoots) became black. This 

 agrees with information, sent me by various correspondents 

 during the last few years, that they had noticed black eggs, of 

 which they sent me specimens, from which they had no doubt 

 they had hatched Hop Aphis. 



These observations, coming from such a high authority as 

 Prof. Riley, give thorough confirmation to the belief previously 



* The paper was read before Section D of the British Association for the 

 Advancement of Science, Manchester, Sept. 3rd, 1887. 



