THE DAVEY INSTITUTE OF TREE SURGERY 
cording to orders and families to which they belong, for the rea- 
son that similarity of habits means a similarity in structure, and 
similarity in structure is the basis for the natural classification 
used in grouping and naming insects. 
8. Classed according to the nature of the injury they inflict, 
the injurious insects fall into the following four classes: 
Borers, or those insects that work under the bark, 
either in the adult or larval stage, and the subject of this 
lesson. 
Leaf Feeders, or the insects that feed upon the leaves, 
either in the adult or larval stage, and consume all or part 
of the tissue of the leaves. This includes the eating in- 
sects, the leaf miners, skeletonizers, case bearers, etc. 
The Sucking Insects, or those that secure their food by 
puncturing the tissue and sucking the juices, whether from 
the bark, leaves or fruit. 
The Gall Insects, or those that cause abnormal growths 
on the different parts of the tree as a result of the injury 
inflicted. This class contains representatives from nearly 
every order of insects. It contains a great variety of 
forms, of which comparatively little is known, especially 
regarding the methods of control. They may affect the 
leaves, twigs, bark, flowers, fruit or roots. 
BORERS 
g. From the nature of the injury they inflict, and their habit 
of working under the bark or within the wood, the borers are the 
most difficult, of the serious shade tree insects, to control. In some 
cases the larve live within the tree for three or more years. This 
makes it difficult if not impossible to study their habits, and also 
protects them to a great extent from their natural enemies. 
10. For the most part, the borers are scavengers, living on 
dead or decaying wood, and are an efficient help to the saprophytic 
fungi in reducing waste material to its natural elements, ready to 
be worked over again by other living organisms. In this way 
some of the borers are a great benefit. 
11. Unfortunately, however, some of the borers, in working 
in decaying trees, came too near to the living tissue, and so devel- 
oped a taste for the fresher living wood. From these a few species 
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