INSECT ENEMIES OF EASTERN FORESTS 329 
larger branches or stems, but these belong to groups of which the larger 
number of species are true twig-inhabiting beetles. 
Most of the species breed in decadent, broken, or cut material. 
Many of them inhabit the lower limbs of coniferous trees, and in so 
doing are a beneficial factor, as they aid in and speed up natural 
pruning, thus contributing to the production of timber clear of knots. 
A few species, however, attack vigorous twigs, as is indicated by the 
appearance of a pitch tube at the point of attack. 
The burrows made by the twig borers are of several types. Most 
of them are constructed just beneath the bark, but several species of 
Myeloborus and Pityophthorus penetrate both the bark and the sap- 
wood, and the egg galleries are excavated in the pith. The burrows 
of the twig borers are of several types—cave, radiate, or pith type. 
The genus Cryphalus Erich. contains small, dull, dark-brown to 
black beetles about 2 mm. or slightly less in length. They occur in 
spruce and fir, either in twigs or small limbs. They are not particularly 
aggressive and usually breed in decadent bark. The burrows may 
be of either the cave or the radiate type. Cryphalus balsameus 
breeds in balsam fir and is widely distributed in eastern Canada 
and the eastern part of the United States, probably throughout the 
range of its host. @C. frazeri Hopk. was described from specimens 
taken from Fraser fir in North Carolina. C. rubentis Hopk. was 
described from specimens taken from red spruce in West Virginia. 
C. mainensis is common in both red and white spruce in Maine and 
northern New York. 
The genus Pityogenes Bedel contains four eastern species, all of 
which breed in the twigs and thin-barked limbs of several species of 
pine. The genus is characterized as follows: Body form usually mod- 
erately stout, pubescence scanty, pronotum asperate in front, not mar- 
gined behind, elytra with rows of punctures, the posterior end exca- 
vated and ornamented with teeth which are much stronger in the 
males. The front of the head in the female may be excavated or 
otherwise modified. The burrows in the inner bark are typically 
radiate and often quite regular. 
Some of the species breed by preference in pine slash, whereas 
others are found most commonly in the decadent lower limbs of grow- 
ing pines. Usually vigorous trees are not attacked, but in some cases 
where the previous presence of slash in an area has bred up an im- 
mense population, the beetles on emerging find little suitable host 
material and are forced to attack young pine trees. In such cases 
many beetles are killed by the resistance of the trees, but if numerous 
enough they eventually succeed in killing some trees. They are un- 
able, however, to maintain their numbers under such conditions, and 
such killing of advanced reproduction in a cut-over area soon ceases, 
except where these young trees are in poor condition. Trees weak- 
ened by drought or transplanting, or injured by ground fires or me- 
chanical means, which might otherwise survive, are frequently killed 
by Pityogenes. 
Control measures against Pityogenes are seldom necessary. ‘The 
upbuilding of large populations in slash should be prevented by 
proper treatment of slash near areas of advanced reproduction, espe- 
cially in years of drought. 
