Insects Bred from American Larch 57 
these parts by P. rufipennis, the association of C. pusillus 
and Hf. picee is not common. 
The burrows of C. pusillus are in the inner bark but are 
seldom on the surface of the sapwood. Usually as has been 
pointed out by Stebbing (1914, p. 500) a thin layer of the 
innermost bark remains between the egg-gallery and the sur- 
face of the wood, so that often infested bark may be stripped 
off without discovering the brood. 
In attacking the bark the beetles seem to assemble in the 
burrow of some other insect in groups or colonies comprising 
from five or six to as high as thirty or more individuals. 
Perhaps the smaller numbers are more common, but several 
examples of colonies of twenty or thirty have been observed 
and recorded in our field notes and several engravings made 
by such groups have been obtained. Two of such engravings 
are especially interesting. One, from spruce (Fig. 12), 
shows twenty-two egg-galleries radiating from the nuptial 
chamber of an abandoned burrow of P. rufipennis, while 
several more originate from the one egg-gallery made by the 
original inhabitant. In another ease taken from lareh 
(Fig. 13) twenty-five egg-galleries of C. pusillus originate 
from the nuptial chamber of P. rufipennis. 
The question suggests itself whether these groups of from 
six to thirty or more individuals represent a family or a 
colony made up of a number of families. Stebbing believes 
that the groups represent family groups consisting of one 
male and six or more females, while other writers are non- 
committal on the subject. With no conclusive evidence upon 
the subject, we are inclined to the view that these groups 
represent colonies of numerous individuals of both sexes. 
We are not prepared to state whether or not this species is 
polygamous, but believe that the relations existing in these 
colonies are more or less indiscriminate. 
Various authors seem to agree in describing the egg- 
galleries of this insect as short, smuous burrows about one- 
half inch long (Packard, 1890, p- 825; Stebbing, 1914, 
p-. 499). Our observations do not entirely agree with these, 
however. Where the beetles are relatively few in number 
