APHIDES. 177 



The second tribe has this nerve once forked. This 

 includes only seven species, and the American Blight 

 Aphis, Schizoneura lanigera, is an example of it. 

 This is known as the Schizoneurince. 



The third tribe has the nerve not forked at all. 

 There are ten species of this: the Lettuce-root Aphis 

 {Pemj)higus lactucarius) is one ; but it is not very im- 

 portant agriculturally. This division is known as the 

 Pemi^higitKB. 



The fourth tribe (the Chermesince) has not got this 

 nerve. There are only eight species : the Pine Apple 

 Gall Aphis of the Spruce Fir {Chermes ahietis), and 

 perhaps the Phylloxera of the Vine, belong to this 

 division. 



The fifth tribe (the Bhyzobiince) is wingless, and 

 found chiefly at the roots of Grass or Corn. 



Thus it will be seen that with some few exceptions, 

 which we need not enter into here, there are clear 

 guiding marks through the perplexities of Aphis 

 arrangement.* 



It has been well said, " Differences in structure 

 show differences in habits ; " and where we can lay 

 our hands on some simple points like this, by whicli 

 we can sort a mass of confusion into five well-marked 

 divisions, it is well worth while to master the detail. 



The life-history of the chief division — the A})hidin(e, 

 with the tivo-forked nerve, those which chiefly frequent 

 our crops — may be given generally thus : — The wing- 

 less females, which are produced very soon after the 

 males in autumn, lay eggs ; sometimes singly, some- 

 times in clusters. From these eggs, in the following 

 spring (or possibly before), J'oung Aphides hatch, 

 which are all females : they go quickly through their 

 changes up to the perfect state, and then they pro- 

 duce living young, which also are all females. These 



* Such as are interested in making a thorough study of Aphis Hfe 

 are referred to 'British Aphides,' by G. B. Buckton, F.K.S., 1 vols., 

 published by the Ray Society ; a long and valuable work, which 

 places the subject in a form which can be understood. 



