ILLINOIS TREES AND SHRUBS: 



THEIR Insect Enemies 



L. L. ENGLISH 



Regardless of their size or cost, trees and shrubs used as orna- 

 mentals may be highly prized by their owners as sources 

 of shade or beauty. An important aspect of the care of orna- 

 mentals is the prevention of insect damage. Such plants may be 

 severely damaged or even destroyed unless their owners have at 

 least an elementary knowledge of insect pests and the ways in 

 which they can be controlled. To provide help in the recognition 

 of insect pests of trees and shrubs used as ornamentals and to 

 suggest specific measures for control of these pests is the pur- 

 pose of this circular. 



Insects may damage trees and shrubs in many ways. A col- 

 ony of ravenous caterpillars may strip the foliage from twigs 

 and branches; hordes of aphids may suck the sap from new 

 shoots and leaves, causing them to wilt or to grow abnormally; 

 tiny scale insects may encrust branches and twigs, withdrawing 

 enough food to kill plants outright; borers of many kinds may 

 invade the bark and wood, seriously injuring or killing plants; 

 more subtle but as serious is the damage caused by those insects 

 that carry fungus or virus diseases. 



ABOUT INSECTS 



The first essential for effective control of insect pests is vigi- 

 lance and an interest, which may be acquired, in looking for in- 

 sects and signs of their damage. To detect the presence of 

 insects before they cause serious damage to valuable trees and 

 shrubs, one should carefully examine the plants at least once a 

 week during the growing season. One should examine deciduous 

 trees in winter, also, when scale insects on them may be seen 

 more easily than when trees are in leaf. 



The second essential is at least an elementary knowledge of 

 insects and the ways they reproduce and grow. For example, 

 one should know that while most kinds of insects lay eggs, some, 

 like most of the aphids, give birth to living young. The eggs of 

 insects are of various sizes, shapes, and colors ; most of them are 

 small in size and are not easily seen. They are laid singly or in 

 clusters, hidden or in conspicuous places. With few exceptions, 



