56 College of Forestry 
The European host trees as listed by Niisslin (1913, 
pp. 259) are spruce, pine, fir and larch. E. P. Stebbing 
(1914, pp. 498) adds blue pine (Pinus excelsa) and spruce 
(Picea morinda) from India. In America the host trees 
recorded are: white pine, balsam fir, hemlock (Packard, 
1890), pitch pine, scrub pine, yellow pine, table mountain 
pine, black Seater and Norway spruce (Hopkins, 1893, 
1899). 
This minute ber beetle, one of the smallest of our seo- 
lytids, has a very characteristic habit. It usually gains 
entrance to the inner bark in which it constructs its breed- 
ing quarters through some previously made opening. ‘This 
is usually either the entrance hole or exit hole of the aban- 
doned burrow of some other scolytid. However, a number 
of cases have been observed in which the burrow utilized in 
this manner was still occupied by its original constructors 
and their brood. In several other cases newly started colo- 
nies of C. pusillus were observed which were constructing 
their breeding quarters in balsam fir as an off-shoot from the 
mines of small larvae of Monohammus scutellatus. In these 
latter cases the so-called “ ventilation openings” through 
which the coarse ‘‘ sawdust” of this sawyer is extruded 
served as the place of entrance. 
However, in most cases access to the inner bark is obtained 
through the burrows of another scolytid. Thus it appears 
always to enter the bark later than other bark borers and 
often does not enter until a season later. In larch it was 
found most frequently making its engravings from the aban- 
doned burrows of P. rufipennis, although it was also asso- 
ciated with those of D. simplex and H. picew in a lke 
manner. In several cases it was found associated with the 
living brood of the two former of the species mentioned. 
The brood of this insect have never been taken by us from 
really dry bark, but always from bark containing consider- 
able moisture. For this reason it is to be found associated 
with the burrows of H. picew only in the thicker barked 
regions of the trunk, and as this latter is usually prevented 
from breeding in such places by the earlier preemption of 
