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 this 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 Carolina, 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 lines 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 
feet board measure of the 147,720 feet board measure of standing 
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 FOR 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 bilineatus Web. 
6 See list of publications, page 11. 
¢ The average life of achestnut pole is eight to ten years (Sherfesee and Weiss, 1909). 
