greater destruction to trees through the opportunities that the dead, 
dying, or injured trees afford for the propagation of injurious insects. 
It should be borne in mind that wood and bark-boring insects gen- 
erally prefer timber that has been recently killed, and that when this 
is not available they will attack injured, weakened, or even healthy 
growth. 
It is thus quite possible that we may, within the next year or two, 
hear of a similar invasion to that experienced afew years ago. As the 
two-lined chestnut borer, by which name wemay know Agrilus biline- 
atus, is a species very likely to cause injury in the immediate future, 
it has been chosen as the subject of the present circular, and the mat- 
ter here presented is, in the main, a compilation of facts published in 
a former article by the writer in Bulletin No. 7, n.s., of this Division. 
REPORTED INJURY TO CHESTNUT TREES. 
A few of the more important instances of reported injury to chest- 
nut trees may be enumerated herewith. In 1891 an instance was 
reported from Botetourt County, Va., which, it is more than probable, 
was due, in part, to the species in question. The following year 
the two-lined chestnut borer was found to be injurious in the District 
of Columbia. In 1893 serious injury was reported to the chestnut in 
Fairfax County, Va., about 75 per cent of the chestnut trees, it was 
estimated, having been killed by this insect in that and adjoining 
counties. It was then too late for investigation looking toward reme- 
dial experiment, but certain facts were gained concerning the insect 
and its damage, which will be summarized under another heading. 
During the same year specimens of the work of this insect in oaks 
were brought to the writer’s attention from Richmond, Ill. Similarly 
affected trees were noticed at the same time by Mr. G. B. Sudworth, 
of the Division of Forestry of this Department, in the neighborhood 
of Ann Arbor, Mich., and other cases of injury were reported by 
Dr. A. D. Hopkins, entomologist of the West Virginia Agricultural 
Experiment Station, in and around Madison, Wis. 
PREDISPOSING CAUSES OF INJURY. 
There has always been a certain degree of skepticism as to whether 
perfectly healthy forest growth would, save in exceptional cases, suc- 
cumb to insect attack. There is more often a predisposing agency at 
work to cause a weakened condition of the trees. Whatever brought 
this about in the cases reported, there is every appearance that the 
insect in question multiplied in such numbers that it was forced to 
attack living, if not healthy, plants or perish, as it belongs to a group 
that does not develop in timber which has been dead long enough for 
the bark to become separated from the wood. . 
Such an enfeebled condition as suggested might be caused by bac- 
terial or fungous disease; or it might be due to a variety of other 
