Insects of Shade Trees and Their Control. 73 
Evidence of infestation—The presence and work of the hickory 
barkbeetle are indicated in several ways: (1) Bases’ of twigs, buds, 
and fallen hickory leaves in the spring show signs of having been 
eaten by insects (fig. 51); (2) clear-cut, round holes occur in the 
bark; (8) in August and September the foliage of hickory is faded 
and dying; (4) the inner bark of hickory trees and the wood surface 
beneath it are engraved with peculiar centipede-shaped designs (fig. 
52), consisting of a broader, central, straight, upright gallery with 
narrower burrows radiat- 
ing like centipede legs from TT | 
either side of it. | , | | ( 
History of seasonal ac- Ui | | Ul 
tivity About the time the a Ses 
pollen is falling from the = 
tassels of healthy hickories 
the beetles mate and each 
pair starts the excavation of 
an upright gallery. In 
niches along the sides of 
these, eggs are laid which 
hatch into the grubs that 
tunnel out the “ centipede 
legs.” Until the larve are 
about half grown they feed 
in the-inner layers of 
bark; later they tunnel into 
the middle and outer layers 
of it and pass the winter 
there. In the following 
spring they change to pup 
and then to adults, which 
emerge soon thereafter, thus 
completing the life cycle in 
one year. Retarded de- - Fig. 52.—Work of the hickory barkbeetle on sur- 
velopment of some indi- face of wood beneath bark. a, Primary or egg 
$ gallery; b, larval mines. (Hopkins. ) 
viduals and accelerated de- 
velopment of others often complicate the situation so that most often 
all stages of the insect may be found in the same tree at the same 
time. Each barkbeetle brood gallery cuts that much of the sap flow 
between root and top, and when these galleries connect up completely 
around the trunk the tree is girdled and doomed to inevitable death. 
Natural checks—Like all native insects, the hickory barkbeetle is 
subject to attack in the mature and immature stages by a variety of 
- parasitic and predatory insect and other enemies. By means of 
the sap flow a vigorous hickory tree is also capable of stubbornly re- 
| 
a al 
an 
