6 INSECTS INJURIOUS TO FORESTS. 



in the decomposing wood of various species of deciduous and conif- 

 erous trees, the evidence is abundant that breeding in the bases of 

 chestnut poles is not a newly acquired habit. It has also been 

 determined that tliis beetle damages many species of living forest, 

 fruit, and shade trees that have been previously injured by fire or 

 other causes, and often leads to the destruction of trees that would 

 otherwise recover from such wounds, and while not normally a 

 primary enemy to trees, may thus become of more than secondary 

 importance. 



The damage by the chestnut telephone-pole borer is especially 

 serious in consideration of the fact that in many parts of its range the 

 chestnut is threatened with extinction as a tree species on account of 

 the very severe ravages of the combined attack of an insect " and a 

 fungous disease. Further unnecessary drain upon the supply of 

 chestnut timber should be avoided by protecting that already in use 

 and thus prolonging its length of service. 



EXTENT OF DAMAGE AND LOSS. 



As more than one-fourth of the 3,500,000 round poles exceeding 20 

 feet in length used annually by telephone, telegraph, and other 

 electric companies are chestnut (Kellogg, 1909),* and as this borer 

 has seriously damaged as high as 10 to 40 per cent, varying with 

 conditions of site, of the chestnut poles which have been set in the 

 ground for from ten to twelve years in lines in North Carohna, Virginia, 

 West Virginia, Maryland, and the District of Columbia, it is evident 

 that this insect is an important factor in decreasing the normal 

 length of service of the poles." In hues from twelve to fifteen years 

 old the damage is much greater, and at the end of this number of 

 years of service any line in which poles of this species are set has to 

 be practically renewed. According to a statement in Forest Service 

 Bulletin 78 (Sherfesee, 1909), "approximately 4 per cent, or 5,908,000 

 feet board measure of the 147,720,000 feet board measure of stand- 

 ing poles annually requiring replacement in the United States, is 

 destroyed by insects. ' ' If only chestnut poles be considered , at least 

 10 per cent of the poles reset or replaced are injured by insects. 



FAVORABLE AND -UNFAVORABLE CONDITIONS FOE DESTRUCTIVE WORK. 



The damage is apparently greatest and the borers are most abun- 

 dant where the poles are set in high or level dry ground under good 

 conditions of drainage. Such sites are the crests of railroad cuts 

 through low hills, slopes of "fills," and in cultivated or other fields. 

 Where the poles are in wet sites there is usually but little injury by 



'^Agrilus hilineatm Web. Yearbook, U. S. Dept. Agr., p. 401, 1909 



''See list of publications, p. 11. 



<: The average life of a chestnut pole is eight to ten years (Sherfesee and Weiss, 1909). 



