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



for the destruction of pines. Their attacks are characterized by large 

 reddish pitch tubes that form at the point of attack. On burrowing 

 under the bark the beetles excavate an irregular longitudinal egg 

 gallery between the bark and the wood. These galleries range from 

 a few inches to several feet in length, as Patterson reports finding 

 one gallery extending underground along a root for 15 feet from the 

 point of entrance. The gallery is more or less packed with frass, 

 and eggs are laid in groups or masses at intervals along the sides. 

 The larvae feed out through the inner bark in mass formation, pro- 

 ducing a cavity between the bark and wood which ranges from a few 

 square inches to a square foot or more in area. These chambers are 

 often filled with a resinous liquid that apparently has no injurious 

 effect upon the developing broods. Transformation to the aduh. 

 stage occurs within pupal cells constructed in the boring dust of the 

 brood chamber or in short mines along its margin. 



There are one or more overlapping generations annually, depending 

 on the locality and season. In the more southern range of the beetles 

 it can be found in all stages of development at nearly any season of 

 the year. The heaviest attacks occur in midsummer, and the winter 

 is passed as larvae, new adults, and parent adults, in trees and stumps 

 attacked the previous season. 



Though this beetle is seldom of serious importance in commercial 

 timber stands, should control measures become necessary, the broods 

 could be destroyed by removing the bark from fresh stumps and from 

 the base of infested trees. For the protection of individual park or 

 shade trees, the damage can be halted by cutting out the attacking 

 beetles w^ith a knife or chisel as soon as pitch exudations indicate their 

 presence. Successful control also has been obtained by injecting 

 carbon disulphide into the galleries. 



THE PINE ENGRAVER BEErTLBS 



Smaller species of bark beetles which work in the trunks and 

 larger branches of pines, and construct egg galleries which radiate 

 from a central nuptial chamber and form distinctive patterns, are 

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

 Ips^ Pityogenes^ Orthotomicus^ and other related genera. 



These bark beetles normally feed on the cambium of w^eakened, 

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

 ing in large numbers in such material as windfalls, snowbreak, 

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

 tonus 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 Dendroctonus 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 associ- 

 ation with Dendroctonus beetles, in which case their attack is usually 

 of a secondary nature, although in some cases, top-killing of trees 



