INSECT ENEMIES OF WESTERN FORESTS 173 



and under the bark and do more or less damage to forest trees, 

 but so far none of the western species have become of sufficient 

 importance to require the application of control measures, and 

 space does not permit listing them here. 



ROUNDHEADED BORERS, OR LONG-HORNED BEETLES 



The roundheaded borers, or long-horned beetles (Cerambycidae) 

 (35), are an important group of forest insects, and include some 

 very destructive species of tree-killing and wood-boring forms. 

 Few of the western species, however, are serious enemies of liv- 

 ing trees, although many species are injurious to forest products. 



The adults are medium- to large-sized, oblong to cylindrical 

 beetles, with antennae often longer than the entire body. These 

 long antennae, or feelers, are their most characteristic feature and 

 give them the name of "long-horned beetles." The name "round- 

 headed 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 distinguishes 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 to living trees, 

 whereas others work in the bark of trees killed by other insects, 

 or breed in the bark of felled, fire-killed, or wind-thrown trees. 

 Some are beneficial in that they feed so voraciously on the bark 

 that they rob the primary bark beetles of their food and thus 

 starve out some of their young. 



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 and are usually packed with the bark or wood fibers 

 of the larval borings. 



So far no attempt has been made to control these species in 

 western forests, and few are ever aggressive enough to warrant 

 such measures. 



The roundheaded fir borer (Tetropium abietis Fall) is probably 

 the most injurious roundheaded bark-boring species in western 

 coniferous trees. The grubs are commonly found working under 

 the bark of felled true firs and are sometimes suspected of being 

 responsible for the death of standing trees. In the adult stage this 

 insect is a velvety brown beetle about % inch in length (fig. 80). 



The western larch roundheaded borer (Tetropium velutinum 

 Lee.) works between the bark and the wood of weakened larch 

 and hemlock and is sometimes suspected of killing such trees. It is 

 distributed throughout the Rocky Mountain and Pacific coast re- 

 gions, where it also is found breeding in Douglas-fir and sometimes 

 in spruce and pine. The adults are elongated, velvety-brown beetles 

 about y 2 inch long and are in flight from May to August. The 

 larvae feed in the bark, where they construct irregular, winding 

 mines which sometimes completely encircle the tree. During the 



