The Pine Beetle. 



73 



autumn or winter. Trees that have been dead longer than the 

 period indicated are not attractive to the insects. All kinds of 

 true pines, such as the Scots Pine, Black Austrian Pine, &c, are 

 used for breeding purposes ; and occasionally, though very rarely, 

 the spruce, larch, and other conifers are also utilised. Trees or 

 boughs of a size to carry thick rough bark are chiefly infested 

 by the insect for purposes of breeding ; young trees, or branches 

 with comparatively thin smooth bark, are largely avoided. The 

 insects pair and proceed to bore into the bark, making a passage 

 between the bark and the wood, the latter, however, being hardly 

 broken. This passage has a slight bend at the starting-point, 

 but afterwards is nearly straight (Fig. 2). It is usually about 



FIG. 2.— MOTHER AND LARVAL GALLERIES, SHEWING TWO AIR-HOLES, NATURAL 

 SIZE. THE MALE KEEPS NEAR THE ENTRANCE, WHILE THE FEMALE 

 CARRIES ON THE WORK OF EXCAVATION. 



four inches long, and is generally supplied with one or more air- 

 holes besides that by which the pair of insects entered. In 

 making this gallery the dust is thrown to the outside, where 

 its presence quickly attracts the attention of an experienced 

 observer. 



As the gallery is proceeded with the female beetle lays about 

 100 eggs, depositing them alternately on either side, and these 

 produce larvae in about a fortnight. The larvae proceed to eat 

 into the inner bark (bast) at right angles to the main passage, 



