Insects Injurious to the Apple. 131 



physiological changes take place in the attacked shoots and leaves 

 have never been investigated. Why the leaves should, as is fre- 

 quently noticed, hang on the trees instead of falling normally, has 

 not been explained. This is a very marked character in trees that 

 have been infested with Aphis pom i, De Geer. 



With a few exceptions the chief aphides on apple trees have 

 been seen to belong to three species, Aphis j^oini, I)e Geer,* Aphis 



* This has usually been known as Aphin uiaJi, Fabricius 177"), but De Geer 

 had previously described it as Aphis jjniiii in 177o. 



