176 APHIDES, SCALE INSECTS, ETC. 



but in some cases the male has not yet been observed,, 

 and sometimes there are only wmgless females ; like- 

 wise in some cases, as with the Phylloxera vastatrix 

 of the Vine, there is a variety of form between the 

 kind that lives under ground on the roots, and above 

 on the shoots or leafage. 



There is so much difficulty in the study of Aphides, 

 and often such unnecessary trouble and confusion of 

 mind as to what we need to know for practical use, 

 that before going on I wish to direct attention to a 

 few points which may be of practical assistance. 



There is one large tribe of Aphides (such as we 

 know, on the Hop, Turnip, Plum, &c.) containing 

 upwards of 150 British species. There are also four 

 very much smaller tribes, which live in various ways. 

 Three of these may often be known by the kind of 

 diseased growths they cause, such as the American 

 Blight of the Apple, the swollen bag-like leaves of the 

 Elm, or the Pine Apple-like Galls of the Spruce Fir ; 

 and one of the tribes feeds on roots under ground. 



The first four of these five families may be known 



by a difference in the veining of the wings ; and the 



fifth, which is a root-feeder, by never having (so far 



as I am aware is known at present) any wings at all. 



If we look at the foremost wings of an Aphis, we 



shall see that there is one 



strong nerve or vein runs 



down it, near the front edge. 



If we now begin at the body, 



and count the side nerves 



^ ,„„ ^ . . that start from this front 



Fig. 137.— Fore wing ot ,, 



Aphis, of division of AjpMcUme. ncrvc, — ouc, two, thi ee, — 



we shall find at the thnxl 

 nerve that, in the Turnip, Hop, Bean, or many others 

 of our crop Aphides, this third nerve branches again 

 into two forks. 



All Aphides with these two forks to the third nerve 

 belong to one great tribe, known as Apliidiiue, and 

 have (as far as we can tell from those that have been 

 studied) the same kind of life-history. 



