INSECT ENEMIES OF WESTERN FORESTS 135 
name of “long-horned beetles.” The name “roundheaded borers” 
comes from the structure of the larvae, which are white, long, slender, 
usually legless grubs with enlarged thoracic segments, and with a 
horny plate on the top surface of the first segment near the head, 
but with no plate on the under side of this segment. This distin- 
euishes them from the flatheaded larvae, which in most species have 
a plate both above and below. 
While many of the species are characteristically wood-boring in 
habit, one group confines its work to boring beneath the bark. Some 
of these bark-boring 
species are injurious 
LO iv Meo sb Ie eS, 
whereas others work 
in the bark of trees 
killed by other in- 
sects, or breed in the 
bark of felled, fire- 
killed, or wind- 
thrown trees. Some 
are beneficial in that 
they feed so vora- 
ciously on the bark as 
to rob the primary 
bark beetles of their 
food and thus reduce 
their progeny. 
The adults deposit 
their eggs in bark 
crevices, and the 
young larvae bore 
through the bark 
and construct long, 
irregular mines in 
the bark and wood. 
These are increased 
In size with the 
growth of the larvae Figure 66.—Roundheaded_ fir borer (Tetropium abictis) : 
A, Adult, x 3; B, detail of adult head, side view, x 4; 
and are . usua l ! aye C, larva, X 2; D, dorsal view of last abdominal segments 
packed with the bark of larvae x 2; B. pupa, x Pap Hy, cochon of parasitized 
% arva in pupal cell, natural size; G, Ichneumon parasite, 
or wood fibers of the natural size. (Drawing by Edmonston.) 
larval borings. 
So far no attempt has been made to control these species in west- 
ern forests, and few are ever aggressive enough to warrant such 
measures. 
The roundheaded fir borer (Vetropium abietis Fall) is probably 
the most injurious roundheaded bark-boring species in western conif- 
erous trees. The grubs are commonly found working under the bark 
of felled balsam firs and are sometimes suspected of being respon- 
sible for the death of standing trees. In the adult stage this insect 
tae oe brown beetle about three-fourths of an inch in length 
g. 66). 
The western larch roundheaded borer (Z'etropiuwm velutinum Lec.) 
works between the bark and the wood of weakened larch and hem- 
