164 AN INTRODUCTION TO ENTOMOLOGY. 



Owing to the great injury which the species has done to the vine- 

 yards of France, hundreds of memoirs have been published regard- 

 ing it. But, as yet, no satisfactory means of destroying it has been 

 discovered. The difficulty lies in the fact that the insecticide must 

 be one that can penetrate the ground to the depth of three or four 

 feet, reaching all of the fibrous roots infested by the insect. It 

 must be a substance that can be cheaply applied on a large scale ; 

 and it must also be something that will kill the insect without injury 

 to the vine. 



Where the vineyards are so situated that they can be submerged 

 with water for a period of at least forty days during winter, the 

 insect can be drowned. But this method is obviously of limited 

 application. 



It is found that vines growing in very sandy soil resist the attacks 

 of the Grape Phylloxera. This is supposed to be due to the diffi- 

 culty experienced by the insect in finding passages through such 

 soil. 



The method of destroying the pest which is most generally avail- 

 able is by the use of carbon bisulphide. See Chapter XIV. 



Sub-Family III. PEMPHIGIN^E.* 



The Pemphigince includes those genera of plant-lice in which the 

 front wings have three discoidal veins, and of which the third dis- 

 coidal vein has only one fork or is simple ; the honey-tubes are 

 tuberculiform or wanting. 



In habits and transformations it is an unusually interesting group. 

 As a rule the species live above ground, although with some there 

 are root-inhabiting forms. Many species are remarkable for the 

 form and abundance of their excretions ; others cause abnormal 

 vegetable growths or galls within which they live. The galls made 

 by the different species vary greatly in form ; but each species pro- 

 duces a characteristic gall. 



The species chosen to illustrate this sub-family represent two 

 sections of it, as indicated below : 



Section I. PEMPHIGINI. 



This section includes genera in which the third discoidal vein of 

 the front wings is simple ; the antennae are six-jointed. 



* Pemphiglnae, Pemphigus: pemphix (Ttejufiig), a blister. 



