56 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
The Monterey pine resin midge (etinodiplosis resinicoloides 
Wms.) is another small pitch midge which inhabits the resin exuda- 
tions of Monterey pine but apparently is not injurious to the trees. 
FEEDERS ON THE INNER BARK OF YOUNG TREES 
The most frequent damage to young trees by insects that feed on 
the inner bark is that suffered by intermediate or suppressed trees 
growing under crowded conditions or those weakened by drought, 
fire, or mechanical or other i injury. Vigorous, young, dominant trees 
in the stand have a good chance to escape damage from these insects, 
except under conditions where they become epidemic. Usually the 
normal damage of this character in the virgin forests is of more 
benefit than otherwise, since it represents a natural thinning process 
and the release of the more dominant trees from competition. At 
times, however, such damage may become serious when outbreaks of 
bark beetles or other cambium- or root-feeding insects sweep through 
the young stands and kill a high percentage of thrifty as well as 
weakened individuals. 
The insects which feed on the inner bark of trunk or roots of 
young trees are usually those which also feed on thin bark of older 
trees. These include certain groups of bark beetles, bark borers, and 
bark weevils. Since most of these insects do their greatest damage 
to older, mature trees they will be discussed later under another 
heading ‘(p. 95) 
Many species of bark beetles (Scolytidae) inflict their greatest 
damage on small or thin-barked trees. Many of these are rarely, if 
ever, primary and aggressive in their attacks upon large trees, but 
may breed in windfalls, slash, or large trees that are dying or have 
been attacked first by other bark beetles. Breeding in such trees or 
felled material, they may emerge in large numbers and become very 
destructive to the small trees in the stand. 
In pines, the pine engraver beetles of the genus /ps are the ones 
most frequently responsible for this type of damage. Less frequently 
species of Pityogenes or Pityophthorus are involved. 
In young stands of Douglas fir Pseudohylesinus nebulosus Lec. 
and Scolytus unispinosus Lec. frequently kill groups of small trees, 
particularly in the vicinity of slashings. 
Small balsam firs are similarly affected by species of Scolytus, 
Pseudohylesinus, and Pityokteines. Young spruce and hemlock also 
may be killed by species of these and other genera. 
Young redwoods, cedars, cypresses, junipers, and related cupressine 
trees are frequently killed by species of Phloeosinus, which breed 
in the trunks and limbs of dying or dead larger trees. 
DEFOLIATORS OF YOUNG TREES 
The insects that feed upon the leaves of young trees are in nearly 
every instance the same species as those that feed on the leaves of 
older trees. Defoliating insects usually show no particular choice as 
to the age or size of tree that they attack, and young trees in the 
forest may be fed upon by almost any leaf-feeding form. In some 
cases the young trees in the stand are actually avoided by defoliating 
insects. ‘This was particularly noticeable in the case of the hemlock 
