150 TREES IN WINTER 



completely defoliated without being killed. When the foliage is 

 destroyed early in the season a second crop of leaves usually ap- 

 pears. The necessity for furnishing a second supply of leaves 

 in one season weakens the tree, and if it is repeated for three or 

 four years, is likely to prove fatal. The condition becomes more 

 serious when the second crop of foliage is also destroyed. Without 

 foliage the tree cannot store up the necessary reserve material to 

 supply its needs the following spring. 



Another class of insects, mostly grubs, cause injury by burrow- 

 ing under the bark and into the wood of trees. These are the 

 so-called borers. Occasionally one of these insects, like the Maple 

 borer, will completely girdle and cause the death of a tree in one 

 season, but usually they will work in a tree for many years before it 

 dies. The insects so weaken the trees that they are finally blown 

 over or broken down. To this class of insects belong some of 

 our more serious pests. Their destructiveness is because of their 

 habit of attacking a tree at its most vital point — the cambium — 

 and because their presence is not often detected until much dam- 

 age has been done. Even when they are known to be present they 

 are destroyed with great difficulty. 



A third class of insects, including the bugs, scales, and plant lice, 

 injure the trees by piercing the tissue and sucking the juices. The 

 affected foliage becomes pale in color, curls up, and sometimes dies. 

 The bark also becomes infested and often large pits or indentations 

 are formed. With most members of this class, their great power 

 for destruction lies in their appearing in such enormous numbers 

 and in their power to reproduce so abundantly. Of the San Jose 

 scale, for example, there are three or four broods in a season, and 

 one pair of insects surviving the winter may by fall have progeny 

 numbering into the billions. 



Methods of Comhatting Insects — In the control of insect pests 

 it is necessary to know something about their feeding habits. The 

 failure to get satisfactory results from spraying may usually be at- 

 tributed to the use of the wrong remedy. In the control of insects 

 that obtain their food by sucking, no benefit would be derived from 

 the application of stomach poisons, for it would be impossible to 

 get any of the poison into the insects' food. It is necessary, 

 therefore, to first determine to which class the pest belongs — 

 whether it is a chewing-insect or a sucking-insect. 



