INSECT ENEMIES OF WESTERN FORESTS 



31 



of attack on the twig. Under this will be found small tunnels of 

 uniform width, free from packed boring dust, which are made by 

 small brown to black beetles. From egg niches along the sides of 

 the egg tunnels, larval mines extend under the bark. These are made 

 by small, white, curled, legless larvae that leave fine, packed boring dust 

 behind them. In many cases several egg tunnels start from a circular 

 entrance chamber under the bark and run lengthwise of the stem. 



This type of work may 

 be done by members of sev- 

 eral genera of bark beetles 

 represented by hundreds of 

 species, so only a few of the 

 more common species can 

 be mentioned here. More- 

 over, there is no well-defined 

 dividing line between* the 

 species that work in twigs 

 and those that work in the 

 larger limbs, branches, and 

 trunks. Some species maj- 

 be found breeding in all of 

 these places ; so, in addition 

 to the species listed in this 

 section, those described un- 

 der the heading of ''Bark 

 beetles" on page 96 should 

 also be considered. 



The control of twig 

 beetles has never been at- 

 tempted in western forests, 

 as their damage is seldom 

 serious enough to warrant 

 control measures. If they 

 are especially bad in planta- 

 tions or on shade trees, prun- 

 ning the infested branches 



and buring the twigs may figure 12.— The Douglas fir twig beetle {Pityophtho- 

 Vio r»-f crkTYio l^oi->ofif *"^*^' pseudotsugae Syv.) and character of its work in 



ue uj. buiiie ueiieiiL. mountain hemlock. Natural size. 



Pine Twig Beeitles 



There are a large number of twig beetles that work under the bark 

 and in the pith of pine twigs and sometimes in larger branches and 

 even in the trunks. These species develop readily in slashings and 

 broken twigs, and frequently cause the death of twigs and limbs on 

 living trees. The twig beetles most frequently found attacking pines 

 belong to the genera Pityophthorus^ Pityogenes^ Pityohorus^ Pityo- 

 fhilus^ MyelohoTus^ Carjyhohorus^ Orthotomiciis^ and Ips (p. 110). 



The typical work of the Pityophthorus (S) consists of a central 

 nuptial chamber under the bark, from which radiate several egg gal- 

 leries each occupied by a female beetle (fig. 13). Eggs are placed 

 in large niches along the sides of these egg galleries, and the larvae, 

 on hatching, work through the cambium of the twig and, on reaching 



