INSECT ENEMIES OF WESTERN FORESTS 37 



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. On many trees 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 several genera 

 of bark beetles represented by hundreds of species, so only a few 

 of the more common species can be mentioned here. Moreover, 

 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 may be found breeding in all these 

 places; so, in addition to the species listed in this section, those 

 described under the heading "Bark Beetles" (p. 129) should also 

 be considered. 



The control of twig beetles has never been attempted in western 

 forests, as their damage is seldom serious enough to warrant con- 

 trol measures. If they are especially bad in plantations or on shade 

 trees, pruning the infested branches and burning the twigs or 

 spraying with DDT may be of some benefit. 



PINE TWIG BEETLES 



Many twig beetles 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 deaths of twigs and limbs on living trees. 

 The twig beetles most frequently found attacking pines belong to 

 the genera Pityophthorus, Pityogenes, Myeloborus, Carphoborus, 

 Orthotomicus, and Ips (pp. 143-154) . 



The typical work of the Pityophthorus consists of a central 

 nuptial chamber under the bark, from which radiate several egg 

 galleries 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 full growth, pupate at the end of the larval mines, 

 often in the wood or pith of small twigs. There are usually two 

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

 with the locality. Over 100 species have been described from 

 western pines. A few of the more common western species 

 include P. confinis Lee, which attacks ponderosa, Jeffrey, and 

 Coulter pines throughout the West; P. nitidulus (Mann.), found 

 attacking spruce and pines along the Pacific coast from Alaska 

 through California; P. carmeli Sw., which sometimes is very 

 abundant and destructive to Monterey and other pines along the 

 coast of California; P. confertus Sw., which is commonly found 

 attacking lodgepole, ponderosa, and many other pines throughout 

 the West; and P. tuberculatus Eichh., which is also widely dis- 

 tributed in range and hosts. 



The species of Myeloborus construct their egg tunnels prin- 

 cipally in the pith of pine twigs. The larvae bore into the wood, 

 without making definite larval mines, and so destroy the interior 

 of the twig as to cause its death. In general, their work is bene- 



