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



frequently referred to as the pine engraver beetles. These belong to 

 Ips, Pityogenes, Orthotomicus, and related genera. 



These bark beetles normally feed on the cambium of weakened, 

 dying, or recently felled coniferous trees and are capable of de- 

 veloping in large numbers in such material as windfalls, snow- 

 break, logging and road slash, and also the tops of trees killed by 

 Dendroctoniis or other beetles. They are beneficial insofar as they 

 help in the reduction of forest debris, but if large quantities of 

 favorable host material are available they frequently develop and 

 emerge in such numbers as to attack and seriously injure or kill 

 adjacent groups of healthy trees. Under such conditions they are 

 often exceedingly destructive to seedlings, saplings, and young 

 second-growth poles, and the tops of older trees. While Dendroc- 

 toniis beetles prefer to attack the thick bark of the main trunk 

 and are, therefore, more destructive to mature trees, the engraver 

 beetles usually select thin-bark trees for attack, thereby qualifying 

 as primary enemies of younger trees. Some species are frequently 

 found working in association with Dendroctonus beetles, in which 

 case their attack is usually secondary, although some top-killing 

 of trees by these engraver beetles precedes and possibly attracts 

 subsequent infestation by Dendroctonus beetles. With the removal 

 of mature forests, some authorities consider it likely that this 

 group of bark beetles will outrank the Dendroctonus beetles in 

 destructiveness to the second crop of pines. 



The first evidence of attack by Ips beetles is yellow or reddish 

 boring dust in bark crevices, or little piles of such dust around 

 the entrance holes or on the ground beneath. Pitch tubes are 

 seldom formed, and the boring dust is usually dry and free from 

 pitch. Within 2 or 3 weeks after a tree has been attacked, the 

 foliage fades and turns from green to yellow, sorrel, and red. 

 Upon removal of the infested bark, the tunnels of the engraver 

 beetles will be found grooving the inner bark surface and, where 

 the phloem is thin, lightly to deeply grooving the sapwood. The 

 egg galleries differ from those of the Dendroctonus beetles in that 

 instead of being tightly packed with boring dust they are open 

 runways in which the adult beetles are free to travel the entire 

 length. A second difference is their polygamous social habit of 

 constructing a central nuptial chamber from which fork or radiate 

 several egg galleries. In many trees the pattern of the completed 

 work is sufficiently distinctive to identify the species responsible. 

 However, some species cannot be recognized in this way and can 

 be distinguished only by characters in the adult beetles. 



The adults are small, reddish brown to black, often shiny, cylin- 

 drical bark beetles ranging from % to approximately y 5 inch long. 

 A distinguishing feature is the pronounced concavity on the pos- 

 terior end, which is margined with three to six pairs of toothlike 

 spines (fig. 65). The small, white, legless larvae differ slightly 

 from Dendroctonus larvae in that the body is more tapering and 

 is thicker at the forward end than toward the rear. 



Attacks are made by these bark beetles with the coming of warm 

 weather in the spring. An adult male bores through the bark and 

 constructs a small cell or nuptial chamber in the inner bark. Sev- 



