85 



CHAPTER III. 



COLEOPTERA SCOLYTID^E (Bark-Beetles). 



From the point of view of forest entomology, one of the most im- 

 portant groups of insects is that of the beetles known as Scolytidae, 

 inasmuch as they are practically all tree-feeders. As a general rule, 

 they attack only dead, dying, or back-going trees, and therefore it is 

 possible that, from a purely economic point of view, their importance 

 may have hitherto been over-estimated by many writers. At the 

 same time, there are a few exceptions to this general rule. For in- 

 stance, in one stage of its life-history Hylurgus (Hylesinus) piniperda 

 attacks the healthy shoots of Scots pine trees ; and Pityogenes biden- 

 tatus often attacks sickly and unhealthy young trees, and thus kills 

 outright what otherwise would have recovered. 



Many of the beetles are exceedingly small in size, which fact, coupled 

 with their minute structural points, makes them of great interest to 

 the working entomological microscopist. 



In a general way the bulk of this family are known as bark-borers, 

 and the Germans consequently call the whole group " Borkenkafer," 

 or bark-beetles. But this is only a general term, for, as a rule, the 

 majority bore deeper, and leave their impressions, or all-important 

 markings, just under the bast, and immediately over the surface of 

 the wood. Others, again, bore directly into the timber, but, as a rule, 

 these wood- boring species confine their attacks entirely to the sap- 

 wood, and rarely penetrate into the heart-wood. Thus we have, in a 

 general way, three divisions viz., those which bore into the bark, 

 those which work on the surface of the wood, and those which bore 

 directly into the timber. So far as classification is concerned, we 

 cannot make any arbitrary divisions, but the characteristic markings 

 themselves are about as suitable data for the discrimination of species 

 as it is possible to get. 



