72 



dom of Plum in early summer after the winged migration therefrom 

 to the Hop. 



^'The observations here recorded have shown (as such minute observa- 

 tions always do) the UDreliability of iuexi)ert testimony. As in Amer- 

 ica, this has been a year of exceptioual freedom from hop-lice in England, 

 and when I first visited the hop-yards at the commencement of the 

 gathering I was told very generally by laborers and owners that no 

 lice had been noted lately, whether on the Hop or on the Damson, and 

 that I should find none. Yet, though the leaves of the Hop were re- 

 markably free, I had no difiQculty iu finding the lice in the burrs, or 

 crawling in all conditions through the loose texture of the sacks which 

 were being filled by the pickers, while the first deposited on Plum were 

 detected on the very first tree examined. 



^' In conclusion, I have been struck with the great similarity in the 

 general aspect of things both on the Hop and the Plum here and in 

 America. Everywhere parasites and predaceous enemies of the lice, 

 belonging to the same or similar genera, and in some instances the 

 same species, and everywhere the omnipresent Red Spider [Tetranychus 

 telarius), and its equally omnipresent spherical reddish eggs at this sea- 

 son. And while the lower average summer temperature will cause 

 fewer generations of the Phorodon to be produced in England (prob- 

 ably only six or seven) than in America (where thirteen have been 

 traced this year), and the beginning and ending of the insect's activity 

 will be more abruj^t there than here, yet in all essential points the life- 

 history of the species in the two countries is the same." 



These facts which I obtained in England were independently con- 

 firmed by my assistants in this country during the same i3eriod, and 

 the correspondence between the facts observed on both sides of the 

 Atlantic has been set forth in a communication to the Country Gentle- 

 man for Xovember 17, 1887, by my first assistant, Mr. Howard, from 

 which 1 quote the following: 



"Professor Riley's observations in England I shall quote in his own 

 words from a communication written to me from Maidstone, October 

 8. The exact correspondence is marked, and is even surprising when 

 we consider the different conditions of temperature and rain fall. 



" ^I shall be able after all to get to the continent without intrusting 

 any one else here with the finale re Phorodon. I have the whole thing 

 complete. Egg laying began not more than two days ago, and with 

 the last two warm, ])leasant days it is going on rapidly, the males being 

 active in fecundation. I have not much time to write, but the fiicts are 

 all as pat and clear as day here. From middle to 2oth of September, 

 while ho[)s were being gathered, the winged females were developing 

 and leaving the hops. On Prunus of all varieties — but particularly on 

 Damson — they settle and begin to feed and produce young. Wiien 

 weather and wind are favorable I have seen tiiem cover trees in two 

 days so that every leaf would have a dozen or more, generall}' heads 



