INSECT ENEMIES OF WESTERN FORESTS 31 
of attack on the twig. Under this will be found small tunnels of 
uniform width, free from packed boring dust, which are made by 
small brown to black beetles. From egg niches along the sides of 
the egg tunnels, larval mines extend under the bark. ‘These are made 
by small, white, curled, legless larvae that leave fine, packed boring dust 
behind them. In many cases several egg tunnels start from a circular 
entrance chamber under the bark and run lengthwise of the stem. 
This type of work may 
be done by members of sev- 
eral genera of bark beetles 
represented by hundreds of 
species, so only a few of the 
more common species can 
be mentioned here. More- 
over, there is no well-defined 
dividing line between the 
species that work in twigs 
and those that work in the 
larger limbs, branches, and 
trunks. Some species may 
be found breeding in all of 
these places; so, in addition 
to the species listed in this 
section, those described un- 
der the heading of “Bark 
beetles” on page 96 should 
also be considered. 
The control of twig 
beetles has never been at- 
tempted in western forests, 
as their damage is seldom 
serious enough to warrant 
control measures. If they 
are especially bad in planta- 
tions or on shade trees, prun- 
ning the infested branches 
and buring the twigs may Ficurr 12.—The Douglas fir twig beetle (Pityophtho- 
rus pseudotsugae Sw.) and character of its work in 
be of some benefit. mountain hemlock. Natural size. 
PINE Twic BEETLES 
There are a large number of twig beetles that work under the bark 
and in the pith of pine twigs and sometimes in larger branches and 
even in the trunks. These species develop readily in slashings and 
broken twigs, and frequently cause the death of twigs and limbs on 
living trees. The twig beetles most frequently found attacking pines 
belong to the genera Pityophthorus, Pityogenes, Pityoborus, Pityo- 
philus, Myeloborus, Carphoborus, Orthotomicus, and Ips (p. 110). 
The typical work of the Pityophthorus (5) consists of a central 
nuptial chamber under the bark, from which radiate several egg gal- 
leries each occupied by a female beetle (fig. 18). Eggs are placed 
in large niches along the sides of these egg galleries, and the larvae, 
on hatching, work through the cambium of the twig and, on reaching 
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