INSECTS INJURIOUS TO THE APPLE AND PEAR 



583 



ticularly water-sprouts, and around wounds or scars on the trunk 

 or limbs. Their presence in these places is always an indication 

 that others are feeding upon the roots, where they cause gall-like 

 swellings, so that the roots soon become a mass of knots and die 

 in a year or two if the injury continues. When badly attacked 

 a tree becomes sickly, the foliage turns yellow, and if not killed 

 outright by the aphides, it falls an easy prey to borers and other 

 pests. Injury seems to be worse on light soils and not so severe 

 on heavy soils. Whether the insect is a native or European 

 species is a matter of dispute. In Europe it is called the " Amer- 



Xlti 



A 32 



FIG. 439. The wooly apple-aphis: at left, apterous viviparous female; 10, 

 fall migrant; 11, over-winter young. (After Gillette and Taylor.) 



ican blight," and was described from Germany in 1801. It has 

 now become distributed all over the world on nursery stock, 

 which forms the principal means of its dissemination. 



Life History. On infested trees aphides will be found in all 

 stages of growth on the roots in early spring. On the trunk, 

 under bits of bark or under the dead bodies of those killed the 

 previous fall, will be found numerous small aphides which have 

 hibernated there, though in the North these may be killed out 

 during severe winters. As the buds begin to open, the aphides 

 on the trunk locate on tender new bark and commence to feed, 

 and many migrate from the roots to the top at about the same 



