E. APHIDS AND SCALE-INSECTS (HEMIPTERA) 



31. (a) THE TURNIP APHIS {Rhopalosiphum dianthi) 



(b) THE WOOLLY APHIS (Schizoneura lanigera) 



(c) THE PHYLLOXERA OF THE VINE {Phylloxera 



vastatrix) 



(a) The Turnip Aphis 



In summer and autumn the leaves of turnips are often infested 

 by innumerable small aphids, which pierce the veins and suck 

 the juices, causing the leaves to curl, and in bad cases to turn 

 yellow and fall off. Associated with the species about to be 

 described, other species, which differ in form and colour, are 

 to be met with on turnips. 



The turnip aphis has a plump oval body of green colour ; 

 when young, its tint is yellowish, and late in the season reddish 

 individuals occur. The body is about 2 mm. long, and swollen 

 with a watery fluid, so that it shrivels up after death to a thin 

 scale. It consists of three thoracic, and nine or more ab- 

 dominal segments, the last of which can only be made out 

 with difificulty. The form first to be described has ho wings. 

 There are three pairs of long and slender thoracic legs ; the 

 tarsi are two-jointed, and end in a pair of claws. The head is 

 flattish in front, furnished with long, tapering, seven-jointed 

 feelers, and prominent compound eyes, just behind each of 

 which is a second and smaller compound eye. The mouth is 

 provided with a three-jointed sucking-tube (answering to the 

 labium) ; it is bent downwards in use, but can be laid along 

 the uwder side of the thorax at other times. The sucking-tube 

 is spl!l along its front face, and lodges three needle-like bristles. 

 The middle one represents the two maxillae, which are firmly 

 held together, while the outer pair are the mandibles. These 

 pointed weapons are employed to pierce the tissues . of the 

 plant, and the tube to draw the juices into the mouth. The 

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