iS8 INJURIOUS AND USEFUL INSECTS 



(b) The Woolly Aphis 



The woolly aphis, or American blight, is a wide-spread pest, 

 which attacks neglected apple-trees, and occasionally spreads to 

 elms or plum-trees. The first indication of its presence is 

 usually the appearance on the boughs of light flocks of fine 

 white threads, looking like shreds of cotton wool. Before 

 long the flocks grow into large masses, which can be seen 

 at a distance of many yards. When closely examined, multi- 

 tudes of small, brown insects are seen among the threads, 

 and the microscope shows that they present the features 

 characteristic of aphids. It must be remembered that 

 other insects, such as some scale-insects, form cottony 

 masses on trees, so that the identification by microscope or 

 lens must not be dispensed with. 



This aphid is distinguished by the absence of the pair of 

 tubes which usually stand out from the fifth abdominal seg- 

 ment. The threads which protect the colony exude in a 

 fluid state from glands opening on the surface of the body. 

 Young feeding aphids of this species have very long sucking- 

 tubes, extending far beyond the end of the body, and looking 

 like tails. The name of American blight perpetuates an 

 impression, never clearly verified, that it was imported 

 from America more than a century ago. A quite distinct 

 species, Aphis mali, is found on the leaves and flowers of 

 the apple. 



The woolly aphis is known in three forms — viz. wingless 

 viviparous females, winged viviparous females, and jvingless ovi- 

 parous females. These last are found in the end of summer ; 

 they are of yellowish colour, and possessing no sucking-tubes, are 

 unable to feed. Each lays a single egg in a crevice of the bark. 



The woolly aphids attack not only the stem and branches, 

 but the roots, causing excrescences to form upon them. They 

 stand cold well, even when exposed to the air, and winged or 

 wingless forms may often be found in the depth of winter. 



The injury done to the tree may be very serious, if the 

 attack is not promptly dealt with. Not only does the aphis 

 consume valuable sap, but the young wood penetrated by its 

 boring tongue becomes first tender and then dry, while the 

 bark cracks, and ugly wounds result. 



