INSECT ENEMIES OF WESTERN FORESTS 



35 



ROOT BARK BEETLES 



A few bark beetles (Scolytidae) have been found apparently 

 killing large seedlings through attack on the roots. Species of 

 Hylastes, Hylurgops, and Pseudohylesinus have been found doing 

 this type of damage (see p. 154). 



INSECTS AFFECTING TWIGS, TERMINAL SHOOTS, 

 AND BUDS 



Injury to leaf buds, succulent terminal shoots, and growing tips 

 may be caused by insects of a number of different groups, such as 

 twig-boring caterpillars, twig weevils, twig beetles, roundheaded 

 or flatheaded borers, or even pitch midges, aphids, and scale in- 

 sects (fig. 11). Such insects show a decided preference for these 



Figure 11. — Ponderosa pines that were young and thrifty but have been 



killed by scale insects. 



tender, growing parts of the trees. The damage they do to the new 

 growth of older trees is much less important than that done to 

 young trees. In the normal forest this type of damage to native 

 trees is rarely extensive enough to be serious, but on cut-over 

 lands and in plantations it is frequently disastrous. 



The seriousness of this type of damage is shown in the sand-hill 

 plantations of the Nebraska National Forest. Two species of pine 

 tip moths (Rhyacionia spp.), which were of little importance in 

 their native habitat, found their way into these new isolated 

 plantations. In the new environment, freed from their native 



