ta 
Insects Bred from American Larch 29 
fewer and fewer in number and those of P. rufipennis become 
correspondingly numerous, until at a height of about twenty 
feet D. simplex no longer occurs and P. “rufipennis j is corre- 
spondingly numerous. 
A somewhat similar condition holds for another bark 
beetle — Hecoptogaster picew. This scolytid breeds most 
often in the thin-barked tops and lmbs of the larch. How- 
ever, sometimes it is also found in the thicker-barked, lower 
trunk, as was the case in Tree X. In this tree it was more 
numerous in the upper trunk and tops, but some brood bur- 
rows containing living brood were found at a distance of 
only a few feet from the ground, where the inhabitants of 
the bark were predominately P. rufipennis. 
Still another bark beetle occasionally found in the lower 
trunk of the larch during the first swumer after the death 
of the tree is Crypturgus pusillus, although this form is a 
more characteristic resident of the bark during the second 
year. This minute beetle seems always to construct its brood- 
burrow as an offshoot from the burrow of some other beetle. 
Usually the burrows so utilized are made by some other 
scolytid — in the larch most commonly by P. rufipennis — 
the entrance of this beetle being used in gaining access to the 
inner bark. In other host trees s the entrance burrows of other 
scolytids are often utilized and in Abies balsameus several 
cases have been observed where the tunnels of Monohammus 
scutellatus had been so invaded, entrance to the burrows 
being gained by way of the “ ventilation openings ” through 
which the “ sawdust ” of this sawyer was cast out. In the 
larch, however, the only species with which Crypturgus has 
been observed to associate itself are P. rufipennis and D. 
simplex. 
Several species of predaceous beetles were found associated 
with these scolytids in the bark. The most common of them 
is the ubiquitous Phyllobaenus dislocatus, which is the most 
common clerid beetle bred from wood infested by bark-boring 
insects in this region. It has been found associated with all 
four species of bark beetles mentioned above, and specimens 
of larvae as well as adults have been taken from bark infested 
