180 APHIDES, SCALE INSECTS, ETC. 



stunted, or the Aphides themselves are so numerous,, 

 that it may be presumed the nature of the sap is 

 different to that in the full flow of the healthy shoot, 

 or the Aphis is rather shortened of its food. Neces- 

 sarily, maturity coming sooner, the successive broods 

 are more rapidly produced, and the numbers greater. 



Fig. 139. — ApJiis liumuli : winged and wingless viviparous females, 

 magnified. 



Where we can tell with certainty that some species 

 of Aphis migrates at a special season, from one kind 

 of plant or tree to another, we have a most serviceable 

 method of prevention in our hands. 



It does not seem now to be open to doubt that a 

 great part of the yearly attack of Hop Aphis, or "Fly," 

 comes on the wing from Sloe, Damson, or plants of 

 the Plum tribe. Tbis was long ago stated by German 

 entomologists, also laid down by at least some of our 

 Hop-growers ; and in 1884, after careful examination 

 of specimens of Aphides both from Hop and Plum, 

 and reports from Hop-growers (noted at length with 

 figures in my Pieport for that year), I mentioned that 

 there appeared to me to be reason to believe that the 

 great attack, which usually occurs in the form of 

 "Fly" about the end of May, comes on the wing from 

 Davison and Sloe, as well as (which at this present 

 date of writing I still think is to some extent the case) 

 from Hop. 



