20 BULLETIN 1060, U. S. DEPARTMENT OF AGRICULTURE. 
to heal over scars or wounds along the bole ; here the spores of fungi 
soon establish themselves and, on account of the very moist condi- 
tions in spruce stands, cause the rapid decay of much sound wood. 
Advance rot spreads quickly in this species, and, though often 
hard to detect, it becomes very noticeable after lumber is dried. It 
is commonly, though not always, accompanied by a change of color 
in the wood, appearing as streaks of red, yellow, or green. Tests 
were made recently by pathologists to show the effect of different 
stages of decay on the strength of the wood, particularly for spruce 
airplane stock, but these data are not yet available for publication. 
INSECTS. 14 
Although Sitka spruce, like other forest trees, is subject to insect 
attacks, it is not so susceptible as most of its associates in the forests 
of the Pacific coastal region. The attacks are naturally more serious 
in pure or nearly pure stands of Sitka spruce than in stands in which 
it occurs in mixture. Damage is caused by three classes of insects — 
bark beetles, defoliators, and borers. The first two classes attack 
standing timber and the last works in felled trees. 
The most important insect enemies of Sitka spruce are the bark 
beetles, of which the most destructive is the Sitka spruce beetle 
(Dendroctonus ooesus). This beetle attacks the living trees and 
kills them by girdling in the cabium layer. In attacking the trees 
the first broods enter the inner bark, of the middle trunk, and those 
which appear later extend the infestation to the base of the trunk 
and even to the larger roots. This beetle also works in the inner 
bark of stumps, logs, and slash of felled trees. Although no exten- 
sive depredations of the Sitka spruce beetle have been found thus 
far, it has been reported now and then that groups of Sitka spruce 
have been killed by its activity. If infestations should ever become 
widespread it would be possible to practice control operations by 
cutting and barking the infested trees before the beetles emerge in 
the late spring. It would not be necessary to burn the bark in this 
work. 15 
From time to time Sitka spruce is subject to the attacks of such 
defoliators as caterpillars, sawfly larva?, and aphids, all of which 
destroy the needles and may therefore occasionally kill trees over 
large areas. In Clatsop County, Oreg., in 1890 and 1891, Sitka 
spruce and western hemlock were attacked and killed over an area 
of thousands of acres by a caterpillar belonging to the Geometrid 
family. During the years 1917 to 1920 the Sitka spruce and western 
hemlock on several hundred thousand acres on the Tongass National 
14 Prepared in collaboration with Forest Examiner A. J. Jaenicke, U. S. Forest Service. 
15 For detailed information regarding control measures, see Bulletin 83, Part I. " Bark 
Beetles of the Genus Dendroctonus," by A. D. Hopkins, Bureau of Entomology, U. S. De- 
partment of Agriculture. 
