STREET AND HIGHWAY PLANTING. 



CHAPTER VI. 



INSECTS, FUNGI, INJURIES. 



In many states the problem of the control of insect pests on shade 

 trees is a far more serious one than in the State of California. Of 

 course we are not without our difficulties in these matters, but our 

 troubles are slight compared to the work of the states in many parts of 

 the East. 



It is inevitable, from the interdependence of organisms in nature, 

 that the trees which are used for ornamental planting should furnish 

 food for numerous insects. In natural conditions the trees, by their 

 uneven distribution, may furnish rather scanty food to their insect 

 enemies. Under the artificial treatment of our streets, great numbers 

 of trees of the same species are brought together, and by the care which 

 they receive attain a more uniformly successful development than they 

 might in some natural situations. As we deliberately upset the balance 

 by bringing these trees together and by giving them an opportunity for 

 optimum development, we offer at the same time an opportunity for 

 an abnormal development of the insect pests. That is, in most cases by 

 aiding the growth of the tree, we aid the multiplication of the tree's 

 enemies by making conditions more favorable to their development. 



There are, however, many natural factors which work against the 

 insect's rapid development, just as the insect tends to retard the tree's 

 growth. In the development of the insect from the egg to its adult 

 form there are certain transformations in which the insect passes 

 from one stage of its development into another. Most insects develop 

 from eggs laid by the female insect, which usually selects a place where 

 food will be abundant, to deposit her eggs. The eggs, of course, make 

 no demand upon the plant world, but the young larvae which hatch 

 from the eggs begin feeding almost immediately upon the plants 

 needed for their development. During this stage of development the 

 insect is often as destructive, or more so, than in its adult condition. 

 Caterpillars are familiar examples of this stage of insect life, and illus- 

 trate the preceding statement. The adult condition of the caterpillar 

 is what is known popularly as a butterfly or a moth. As butterflies and 

 moths have mouth parts adapted only to the sucking of liquids, it is 

 obvious that they can not accomplish the damage which the caterpillar 

 may bring about with its strong mandibles for chewing leafy parts. 



During this period of feeding the internal structure of the larva is 

 storing up food and undergoing certain changes which, when they 



