140 STUDIES OF TREES 



and later diluting the product with 5 to 10 gallons of water. 

 It is particularly useful for plant lice in the summer. 



The life history of an insect: In a general way, all 

 insects have four stages of transformation before a new 

 generation is produced. It is important to consider the 

 nature of these four stages in order that the habits of any 

 particular insect and the remedies applicable in combating 

 it may be understood. 



All insects develop from eggs. Fig. 99. The eggs then 

 hatch into caterpillars or grubs, which is the larva stage, 

 in which most insects do the greatest damage to trees. The 

 caterpillars or grubs grow and develop rapidly, and hence 

 their feeding is most ravenous. Following the larva stage 

 comes the third or pupa stage, which is the dormant stage 

 of the insect. In this stage the insect curls itself up under 

 the protection of a silken cocoon like the tussock moth, 

 or of a curled leaf like the brown-tail moth, or it may be 

 entirely unsheltered like the pupa of the elm leaf beetle. 

 After the pupa stage comes the adult insect, which may be a 

 moth or a beetle. 



A study of the four stages of any particular insect is 

 known as a study of its life history. The important facts 

 to know about the life history of an insect are the stage 

 in which it does most of its feeding, and the period of the 

 year in which this occurs. It is also important to know 

 how the insect spends the winter in order to decide upon 

 a winter treatment. 



