32 MISC. PUBLICATION 273, U. 8S. DEPT. OF AGRICULTURE 
full growth, pupate at the end of the larval mines. There are usually 
two or more generations of the beetles each year, the number varying 
with the locality. As over 100 species have been described from 
western pines, no attempt will be made here to list or segregate them. 
The species of IMyeloborus (5) con- 
struct their egg tunnels principally in 
the pith of pine twigs. The larvae bore 
into the wood, without making definite 
larval mines, and so destroy the interior 
of the twig as to cause its death. In gen- 
eral their work is beneficial in that the 
death and dropping of lateral branches 
leaves the trunk of the tree freer from 
knots. In some cases, however, they are 
injurious to small trees. 
Fir Twice BEETLES 
Twigs of Douglas fir and the balsam 
firs are frequently attacked by several 
species and genera of twig bark beetles. 
These usually are secondary enemies, at- 
tacking dying or felled trees, but occa- 
sionally they have been found attacking 
small standing trees in crowded stands. 
The most common species found in twigs 
belong to the genera Pityophthorus, 
Pityokteines, Carphoborus, Cryphalus, 
Crypturgus, Pseudohylesinus, and Sco- 
lytus. 
Species of Pityophthorus and Pityok- 
teines make a central nuptial chamber 
from which several egg galleries radiate. 
One of the most common species is 
Pityophthorus pseudotsugae Sw. (fig. 
Ficurp 13.—Typical galleries ofa 12). Another common species found at- 
Plus Mann) “Natural size, «tacking balsam firs is Pityokteines ele- 
gans Sw. The adults of both species 
are about one-eighth of an inch long, and the females have long, 
yellow hairs on the front of the head. 
Twig beetles attacking spruce and hemlocks usually belong to the 
genera Scolytus, Pityophthorus, Pseudohylesinus, Pityokteines, or 
Ips. 
CeparR Twia BEETLES 
Small twig beetles belonging to the genus Phloeosinus are com- 
monly found working in the twigs and limbs of cedarlike trees, but 
they rarely are numerous enough to cause any appreciable damage. 
In the limbs and twigs of incense cedar are found P. hoppingi Sw., 
P. antennatus Sw., P. fulgens Sw., and P. vandykei Sw. P. nitidus 
Sw. works in Alaska cedar. P. swainei Bruck works in the twigs 
af Sargent cypress in California. 
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