INSECT ENEMIES OF EASTERN FORESTS 191 
The species occurs throughout the Eastern and Central States at- 
tacking chestnut, oak, beech, blue beech, and ironwood. The impor- 
tance of this insect has been the subject of some dispute among en- 
tomologists. ‘There is no doubt that it attacks living trees that have 
sufficient resistance, In many cases, to heal over the galleries which are 
made on the surface of the wood. In fact, the tree frequently repels 
the attack of the insects, killing all the larvae. On the other hand, 
close examination of the host plant always indicates that it had been 
subject to some weakening effect such as root disease, insect defoliation, 
drought, over-grazing, fire, wind, severe frosting, or other causes that 
might ultimately have brought about the death of the tree. Con- 
siderable study by the Bureau of Entomology and Plant Quarantine 
and attempts to control the insect have led to the conclusion that it 
attacks only trees that are severely weakened and that it does no more 
than hasten the death of such trees. Following the droughts of 1930-36 
in the Eastern States, great numbers of dying oaks have been attacked 
by this insect, as well as much beech in northern sections of the country. 
The beetles emerge from the bark of the tree through characteristic 
D-shaped emergence holes in May or June, fly to the foliage where they 
feed for some time, and then deposit eggs beneath the bark scales of 
dead, dying, or weakened trees. The young larvae bore under the 
bark, constructing characteristic zigzag or meandering galleries on 
the wood surface frequently interrupted by a short detour into the 
wood. The pupal cell is finally constructed in the outer layers of the 
sapwood or sometimes in the bark. The attack usually begins in the 
topmost branches. These may be killed the first year, larger limbs the 
second year, and the entire tree may not succumb until the third year 
or later. In the North, two seasons are required to complete develop- 
ment (Chapman, S4). 
Usually no control is practicable, but watering the trees or applying 
fertilizers to stimulate growth may be beneficial or even save some 
trees that have been lightly attacked in the top. As the adults feed 
on the foliage, arsenical sprays or sprays containing DDT (p. 53) 
have been used to protect certain valuable shade trees where cost is no 
factor. 
The bronze birch borer (Agrilus anxius Gory) resembles A. bilin- 
eatus in shape and size, but is uniformly olive bronze. It occurs in 
the north-central and northeastern parts of the United States and 
throughout the Rocky Mountains, attacking dying or weakened 
birches, beech, and aspens. Its life history and habits are very similar 
to those of A. bilineatus, and its economic status in the birch forests 
is regarded as the same as that of b¢/ineatus in oak. It may hasten the 
death of overmature or defective trees left after logging operations 
and of defoliated or drought-affected trees. It frequently attacks 
shade trees and kills them (Slingerland, 387). Pruning back the in- 
fested branches and stimulating growth by fertilizers and watering 
will often prevent the death of the tree. After a tree has been heavily 
attacked, however, control efforts are of no avail (Slingerland, 357 
and Hall, 207). 
There are a large number of species of Ag7ri/us of more or less eco- 
nomic importance, including such forms as A. Jateralis (Say), which 
breeds in the stems of living sweetfern (Comptonia peregrina Coult.) ; 
A. arcuatus (Say), which prunes branches of beech, oak, and hickory, 
792440°—49 13 
