TREES AND SHRUBS 



of the aphides often causes abnormal growths, and it is some of these with 

 which we are concerned in this chapter. 



The Woolly Aphis or Apple Root Louse, often called American Blight 

 (Schizoneura lanigera), causes large warty excrescences on every part of the 

 trunk and limbs of Apple-trees. These swellings are the result of the con- 

 tinuous punctures of the rostra of the aphides, the sap accumulating into 

 soft pulpy masses which harden in winter, cracking in all directions on the 

 surface, and producing scabby hypertrophies or "canker-like" growths which 

 often attain large dimensions. The presence of the aphides in summer is 

 readily apparent from the presence of a white cottony substance formed as 

 an excretion in the back of both young and mature females. The wool some- 

 times hangs in festoons from the trees, and, being blown about by the wind, 

 acts as a means of dispersal of the pest, but the infection is most frequently 

 spread by means of nursery stock. This species is not provided with cornicles, 

 and does not produce honey-dew. The wingless females are purplish-brown, 

 and the lice or larva? are dull yellowish to reddish in colour. The best pre- 

 ventative of the pest is clean cultivation, the trunks and boughs being kept 

 free from lichens and moss, and no rank grass being allowed to grow beneath. 

 In winter the trees may be cleansed of the vegetal encumbrances with a 

 caustic alkali wash, and the trunks may be lime-washed after the removal 

 of all rough bark. 



The Currant Blister Aphis (I.) (Rhopalosiphum ribis) causes convex or 

 concave blisters on the foliage of Currants, red, black, and white, but especially 

 the first. The leaves attacked shrivel away, and the fruit often falls, owing 

 to loss of sap, long before the leaves die. The wingless viviparous female, or 

 " Mother Queen," is shiny green, mottled with darker green, and the cornicles 

 are green. The lice turn to pupa?, from which arise winged, viviparous females, 

 yellowish-green in colour, with black head. Later on the egg-laying female 

 deposits eggs on the twigs, and these hatch in the following spring. This 

 aphis also attacks the Gooseberry, and has been found on the Guelder Rose. 



The Currant Blister Aphis (II.) (Myzus ribis) is distinguished from the 



former by differences in colour in the various stages. The wingless female 



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