110 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
for the destruction of pes. Their attacks are characterized by large 
reddish pitch tubes that form at the point of attack. On burrowing 
under the bark the beetles excavate an irregular longitudinal ege 
gallery between the bark and the wood. These galleries range from 
a few inches to several feet in length, as Patterson reports finding 
one gallery extending underground along a root for 15 feet from the 
point of entrance. The gallery is more or less packed with frass, 
and eggs are laid in groups or masses at intervals along the sides. 
The larvae feed out through the inner bark in mass formation, pro- 
ducing a cavity between the bark and wood which ranges from a few 
square inches to a square foot or more in area. These chambers are 
often filled with a resinous hquid that apparently has no injurious 
effect upon the developing broods. Transformation to the adult. 
stage occurs within pupal cells constructed in the boring dust of the 
brood chamber or in short mines along its margin. 
There are one or more overlapping generations annually, depending 
on the locality and season. In the more southern range of the beetles 
it can be found in all stages of development at nearly any season of 
the year. The heaviest attacks occur in midsummer, and the winter 
is passed as larvae, new adults, and parent adults, in trees and stumps 
attacked the previous season. 
Though this beetle is seldom of serious importance in commercial 
timber stands, should control measures become necessary, the broods 
could be destroyed by removing the bark from fresh stumps and from 
the base of infested trees. For the protection of individual park or 
shade trees, the damage can be halted by cutting out the attacking 
beetles with a knife or chisel as soon as pitch exudations indicate their 
presence. Successful control also has been obtained by injecting 
carbon disulphide into the galleries. 
THE PINE ENGRAVER BEETLES 
Smaller species of bark beetles which work in the trunks and 
larger branches of pines, and construct egg galleries which radiate 
from a central nuptial chamber and form distinctive patterns, are 
frequently referred to as the pine engraver beetles. These belong to 
Ips, Pityogenes, Orthotomicus, and other related genera. 
These bark beetles normally feed on the cambium of weakened, 
dying, or recently felled coniferous trees and are capable of develop- 
ing in large numbers in such material as windfalls, snowbreak, 
logging and road slash, and also the tops of trees killed by Dendroc- 
tonus or other beetles. They are beneficial insofar as they help in the 
reduction of forest debris, but if large quantities of favorable host 
material are available they frequently develop and emerge in such 
numbers as to attack and seriously injure or kill adjacent groups of 
healthy trees. Under such conditions they are often exceedingly 
destructive to seedlings, saplings, and young second-growth poles, 
and the tops of older trees. While Dendroctonus beetles prefer to 
attack the thick bark of the main trunk and are, therefore, more 
destructive to mature trees, the engraver beetles usually select thin- 
bark trees for attack, thereby qualifying as primary enemies of 
younger trees. Some species are frequently found working in associ- 
ation with Dendroctonus beetles, in which case their attack is usually 
of a secondary nature, although in some cases, top-killing of trees 
