PRACTICAL ZOOLOGY 



aphids are always to be found ants which feed upon the drop 

 of " honeydew " secreted by the plant lice. The relations be- 

 tween various kinds of aphids and ants are often very complex. 

 Sometimes the ants cover the aphids with a protecting " shed " 

 of mud (Fig. 23), and it has been shown that the eggs of the corn- 

 root louse are collected by ants in the autumn and stored in their 

 underground nests, where they are cared for until spring when 

 the newly hatched aphids are carried to the roots of the corn. 

 This relationship, termed symbiosis, is mutually beneficial; the 



aphids are pro- 

 tected by the ants, 

 and the ants are 

 repaid for their 

 trouble with hon- 

 eydew. 



CODLING MOTH. 

 - There is one 

 fruit enemy with 

 which every one 

 is acquainted, the 

 codling moth, 

 which is respon- 

 sible for the " wormy " apple (Fig. 24). The eggs of this moth are 

 laid near the apple blossoms, and when the larvae hatch, they crawl 

 to the nearest young apple, into which they burrow. Most of the 

 injured fruit drops to the ground, and when trees are not sprayed 

 with poisonous mixtures, almost every apple is destroyed. The 

 annual loss in the United States due to this pest is about twelve 

 million dollars. 



Insects Injuring Shade Trees. A problem that has been 

 getting more and more serious within recent years is that of 

 protecting the shade trees of city streets and parks. It is now 

 absolutely necessary for the city forester, or those in charge of 

 parks, to be acquainted with the insect pests that feed upon the 

 leaves of trees and to know how to control them. This is es- 



FIG. 24. Codling moth : a, adult ; b, larva in 

 apple ; c, pupa or chrysalis. (From Farmers' Bui. 

 283, U. S. Dept. Agric.) 



