382 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 

 KNOWLEDGE NECESSARY TO PREVENTION OF LOSSES. 



In dealing with the insects mentioned, as with forest insects ^in gen- 

 eral, the methods which yield the best results are those which relate 

 directly to preventing attack. In order to meet with the best success, 

 however, it is necessary to have a complete knowledge of the insects 

 which cause the injuries and the conditions which are attractive to 

 them or otherwise favor their attack, as well as those which are 

 unattractive or unfavorable. 



The insects have two objects in their attack; one is to obtain food, 

 the other is to prepare for the development of their broods. Different 

 species of insects have special periods during the season of activity 

 (March to November) when the adults are on the wing in search of 

 suitable material in which to deposit their eggs. Some species which 

 fly in April will be attracted to the trunks of recently felled pine trees 

 or to piles of pine saw logs from trees felled the previous winter. 

 They are not attracted to any other kind of timber, because they can 

 live only in the bark or wood of pine, and only in that which is in the 

 proper condition to favor the hatching of their eggs and the normal 

 development of their young. As they fly only in April, they can not 

 injure the logs of trees felled during the remainder of the year. There 

 are also oak insects, which attack nothing but oak; hickory insects, 

 cypress insects, spruce insects, and so on, which have different habits 

 and different periods of flight and require special conditions of the 

 bark and wood for depositing their eggs or for the subsequent develop- 

 ment of their broods. Some of these insects have but one generation- 

 in a year, others have two or more, while some require more than 

 one year for their complete development and transformation. Some 

 species deposit their eggs in the bark or wood of trees soon after they 

 are felled or before any perceptible change from the normal living 

 tissue has taken place; other species are attracted only to dead bark 

 and dead wood of trees which have been felled or girdled for several 

 months; others are attracted to dry and seasoned wood; while another 

 class will attack nothing but very old dry bark or wood of special kinds 

 and under special conditions. Thus, it will be seen how important it 

 is for the practical man to have a knowledge of such of the foregoing 

 facts as apply to his immediate interest in the manufacture or utiliza- 

 tion of a given forest product, in order that he may, with the least 

 trouble and expense, adjust his business methods to meet the require- 

 ments for preventing losses. 



DISTINCTIVE CHARACTER OF INSECT INJURIES. 



The work of different kinds of insects, as represented by special 

 injuries to forest products, is the first thing to attract attention, and 

 the distinctive character of this work is easily observed, while the insect 



