INSECT ENEMIES OF WESTERN FORESTS ale 
by these engraver beetles precedes and possibly attracts subsequent 
infestation by Dendroctonus beetles. With the removal of mature 
forests, to some it seems quite likely that this group of bark beetles 
will uranic the Dendroctonus beetles in destructiveness to the second 
crop of pines. 
The Ips or engraver beetles 
The first evidence of attack by this genus is yellow or reddish 
boring dust in bark crevices or little piles of such dust around the 
entrance holes or on the ground beneath. Pitch tubes are seldom 
formed, and the boring dust is usually dry and free from pitch. 
Soon after a tree has been attacked the foneee fades and turns from 
green to yellow, sorrel, and red. Upon removing the infested bark 
the tunnels of the engraver beetles will be found | grooving the inner 
bark surface and slightly marking the sapwood. “The egg galleries 
differ from those of the Dendroctonus beetles in that instead of being 
tightly packed with boring dust they are open runways in which the 
adult beetles are free to travel the entire length. A second difference 
is their polygamous social habit of constructing a central nuptial 
chamber from which fork or radiate several egg ‘galleries. In many 
cases the pattern of the completed work is sufficiently distinctive to 
identify the species responsible. However, some species cannot be 
recognized in this way and can be distinguished only by characters 
in the adult beetles. 
The adults are small, reddish brown to black, often shiny, cylin- 
drical bark beetles ranging from one-eighth to ‘approximately one- 
fifth of an inch in length. A distinguishing feature is the pro- 
nounced concavity on the posterior end, which is margined with from 
one to six pairs of toothlike spines. The small, white, legless larvae 
differ slightly from Dendroctonus larvae in that the body is more 
tapering and is thicker at the forward end than toward the rear. 
Attacks are made by these bark beetles with the coming of warm 
weather in the spring. An adult male bores through the bark and 
constructs a small cell or nuptial chamber in the inner bark. Several 
females then join in the work and each constructs an egg gallery in 
which eggs are laid in niches along the sides. The larvae, upon 
hatching, feed in the inner bark and work away from the egg galler- 
ies, leaving gradually widening, excrement-packed tunnels behind 
them. When their feeding is completed oval pupal cells are formed, 
in which the transformations from larvae to pupae and then to adults 
take place. From the time of attack until the emergence of the first 
of the new brood ordinarily requires from 42 to 68 days. From two 
to five generations of these beetles may develop during the summer, 
depending on the altitude, latitude, and species, there being consid- 
erable overlapping of generations. The winter is usually spent in the 
adult stage, although occasionally i in the egg or larval stage. Some 
species congregate in large groups under the bark of standing trees 
killed the previous year and feed to a limited extent on the dry, dead, 
inner bark. Others emerge and hibernate under the bark of old 
stumps, among the bark scales, or in crevices and litter at the base 
of old brood trees. 
Engraver beetles have a number of predacious and parasitic ene- 
mies but it appears that these do not affect the numbers of the beetles 
