INSECT ENEMIES OF WESTERN FORESTS 



135 



name of "long-liorned 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- 

 guishes them from the flatheaded larvae, wdiich in most species have 

 a plate both above and below\ 



Wliile 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 

 to living trees, 

 whereas others work 

 in the bark of trees 

 killed by other in- 

 sects, or breed in the 



bark of felled, fire- 

 killed, or w i n d - 

 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 w^ i t h the 

 growth of the larvae 

 and are usually 

 packed with the bark 

 or w^ood fibers of the 

 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 {Tetrojnum ahietis 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 

 is a velvety brow^n beetle about three- fourths of an inch in length 

 (fig. 66). 



The western larch roundheaded borer {Tetropium velutinum Lee.) 

 works between the bark and the wood of weakened larch and hem- 



FiGURE 66. — Roundheaded fir borer (Tetropium ahietis) : 

 A, Adult, X ?>', B, detail of adult head, side view, x 4 ; 

 C, larva, X 2 ; D, dorsal view of last abdominal segments 

 of larvae X 2; E, pupa, X 2; F, cocoon of parasitized 

 larva in pupal cell, natural size ; G, Ichneumon parasite, 

 natural size. (Drawing by Edmonston.) 



