162 SHADE-TREES IN TOWNS AND CITIES 



mation of insects is of interest not only to the nature student 

 but also to one who seeks some method of controlling them. 

 There is always some one of the stages in the insect's meta- 

 morphosis when it is most vulnerable and most easily ex- 

 terminated. It may be the egg, larval, pupal, or adult con- 

 dition. It is not usually the time when the most injury to 

 trees is apparent. In insect fighting the point constantly 

 to be borne in mind is, as far as possible, to destroy the 

 pests before they develop and reach their most injurious 

 stage. To do that successfully, a knowledge of the life his- 

 tories of the common tree-pests is absolutely necessary. 



Most States publish bulletins descriptive of the common 

 insect pests of shade and ornamental trees, with directions 

 how to combat them. The state entomologists are always 

 at the service of any citizen and are glad to give information 

 in the matter of insect control. It is therefore thought suf- 

 ficient in this work to- describe only the most common and 

 destructive of our shade-tree pests and point out the easiest 

 means of destroying them. 



There are three classes of tree-destroying insects which 

 may be grouped as leaf -eating insects, sucking insects, and 

 borers. 



LEAF-EATING INSECTS 



Leaf -eating insects inflict injury by feeding on the leaf 

 tissue of plants. They can usually be reached by poison- 

 ing the leasus with an application of arsenic in some form. 



Tussock Moth {Orgyia leucostigma S. and A.). — This 

 insect passes the winter in the egg state. The eggs are 

 deposited by the females in September and October in con- 

 spicuous white masses on the bark of the trees. About the 

 end of May the larvae begin to hatch. They immediately 

 take to the leaves, increase in size and go through five 



