INSECT ENEMIES OF EASTERN FORESTS 295 
and some only in the cones. In the southern pines the cones are at- 
tacked by Conophthorus taedae Hopk.; the terminal twigs by Pity- 
ophthorus pulicarius Zimm.; the smaller smooth-barked limbs by P. 
consimilis Lec. and P. nudus Sw.; the medium-sized limbs by Pityog- 
enes meridianus Blkm.; P. plagiatus Lec., and Ips avulsus Eichh.; 
the upper trunk by /ps grandicollis Eichh., and J. calligraphus Germ.: 
the middle trunk by Dendroctonus frontalis Zimm.; and the lower 
trunk by D. terebrans Oliv., D. valens Lec., and Orthotomicus caelatus 
Eichh. 
Bark beetles also show discrimination as regards the physiological 
condition of the host. Some will breed only in dead or decaying bark 
or wood, others only in dying or recently felled timber, while a few 
prefer trees that appear to be perfectly healthy or are at most only 
shghtly weakened. Species that are habitually found in trees or in 
lhmbs that are slowly dying from suppression are seldom found in 
slash or in vigorous tree tissue. Forms that breed characteristically in 
fresh slash will seldom attack living trees when their favorite ma- 
terial is available. If such forms do attack vigorous trees they suffer 
a high mortality and, although they may eventually kill a few trees, 
their losses are so great that they are unable to continue an epidemic 
in the absence of slash. 
The larvae and adults of the same species usually have similar food 
habits. The ambrosia beetles and their larvae both feed on the fungi 
which invariably grow in their burrows. The wood-eating forms, 
such as Hylocurus, Lymantor, and Micracis in both stages get their 
food from the woody tissues of the sapwood, which may contain con- 
siderable fungous material. The true bark beetles generally construct 
their galleries at the dividing line of bark and sapwood, and their food 
is often derived from both; however, the phloem and cambium usually 
seem to be the main sources of food. 
Young bark beetles, when they have just transformed from the 
pupal stage, are nearly colorless, except for the eyes and mandibles and 
a slight pigmentation at some of the principal leg joints. They take 
little or no food for a day or so, until their chitinous structures have 
hardened somewhat, but then begin to feed actively. It is usually 
from one to several weeks before they attain their mature coloration 
and are ready to leave their original host. When transformation takes 
place late in the summer or in the fall, most species usually remain 
throughout the winter in the host in which they developed, and emerge 
the following spring after several days of feeding. If emergence 
occurs late in the season, some species, such as /ps, and Pityophthorus, 
will not attack new hosts, but will seek hibernation quarters in bark 
crevices, under loose bark, or even in the forest duff. 
Most species on emergence are sexually mature and will attack the 
first suitable material they encounter. Some species, however, must 
feed elsewhere for a time before they are ready to construct their 
brood burrows. The newly emerged adults of species of Scolytus and 
Phloeosinus feed for several days by boring in the bark and sapwood 
of twigs or in the petioles of the leaves of their host plants. Another 
departure from the usual habit is shown by species of Phthorophloeus 
and Leperisinus and by the native elm bark beetle (Hy/urgopinus 
yufipes Kichh.) and others, which emerge from their old hosts in the 
fall, bore into the outer bark of living trees, feed on the sap and 
