32 



MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 



fiill gi^owth, pupate at the end of the hirval mines. There are usuall}^ 

 two or more generations of the beetles each year, the number varying 

 with the locality. As over 100 species have been described from 

 western pines, no attempt will be made here to list or segregate them. 



The species of Myelohorus (5) con- 

 struct their egg tunnels x^rincipally in 

 the 2:»ith of pine twigs. The larvae bore 

 into the wood, without making definite 

 hirval mines, and so destroy the interior 

 of the twig as to cause its death. In gen- 

 eral their work is beneficial in that the 

 death and dropping of lateral branches 

 leaves the trunk of the tree freer from 

 knots. In some cases, however, they are 

 injurious to small trees. 



Fir Twig Beetles 



Twigs of Douglas fir and the balsam 

 firs are frequently attacked by several 

 species and genera of twig bark beetles. 

 These usually are secondary enemies, at- 

 tacking dying or felled trees, but occa- 

 sionally they have been found attacking 

 small standing trees in croAvded stands. 

 The most common species found in twigs 

 belong to the genera Pityophthorus, 

 Pityokteines, Carphohorus^ Ci^phalu^. 

 Crypturg-m^ PseudohyJesinus^ and Sco- 

 Jytus. 



Species of Pityophthorus and Pityoh- 

 teines make a central nuptial chamber 

 from which several egg galleries radiate. 

 One of the most common species is 

 Pityophthorus pseudotsugae Sw. (fig. 

 12 ) . Another common species found at- 

 tacking balsam firs is Pityokteines ele- 

 gans Sw. The adults of both species 



are about one-eighth of an inch long, and the females have long, 



yellow hairs on the front of the head. 



Twig beetles attacking spruce and hemlocks usually belong to the 



genera ScoJytus^ Pityophthorus. Pseud ohylesinus^ Pityokteines^ or 



Ips. 



Cedar Twig Beetles 



Small twig beetles belonging to the genus Phloeosinus are com- 

 monly found working in the twigs and limbs of cedarlike trees, but 

 they rarely are numerous enough to cause any appreciable damage. 

 In the limbs and twigs of incense cedar are found P. hoppingi Sw., 

 P. aiitennatus Sw., P. fulgens Sw., and P. vomdykei Sw. P. nitidus 

 Sw. works in Alaska cedar. P. swainei Bruck works in the twigs 

 of Sargent cypress in California. 



Figure 13. — Typical galleries of a 

 pine beetle (Piti/ophthonis niti- 

 dulu-s Mann.) Natural size. 



