282 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



\oung plants up to live or so years of age are chiefly attacked, 

 pieces of bark being eaten away into the cambium. Flow of sap or 

 resin follows the injury, the latter being often very conspicuous. 

 They cannot do serious injury to old bark, consequently the 

 damage done to trees over ten years of age is usually insignificant. 

 The preventive measures consist in keeping the ground free from 

 unbarked logs and trunks, heaps of rubbish and of sawdust, and 

 in preventing egg-laying in the stools of recently-felled timber. 

 This is done by barking the exposed part, covering with soil, and 

 beating firmly down. 



Hylesinus jnniperda — Pine Beetle. 



This beetle is, next to the UyLohius abietis, the most injurious 

 insect to pines over the greater part of Scotland. It is a small, 

 oblong beetle of brown colour. The pine beetle swarms very early, 

 as early as March in good weather, or in April if it is less favour- 

 able, and deposits its eggs under the bark of newly-felled stems, 

 also in standing trees of sickly growth, selecting as far as possible 

 only the portions of the tree where the bark is thick. It, like the 

 pine weevil, prefers fScots fir, but will make use of spruce and larch. 

 The female commences boring under a projecting side where the 

 bark is thick, often on the under side of a fallen trunk if it is free 

 from the ground, and excavates a gallery in the bark, running, 

 with the exception of the entrance which is curved, parallel to 

 the axis of the stem. It is from three to four and a half inches 

 long, and takes from three to five weeks to construct. 



The eggs, which may reach a hundred and twenty in number, 

 are placed in small hollows excavated alternately along its two 

 sides. The bore-holes, by means of which the insects efiect an 

 entrance, are not infrequently noticeable from the yellowish out- 

 flow of resin on the bark. The eggs hatch in a few days, and the 

 larvae begin to eat galleries at right angles to that of the mother. 

 The larval galleries are at first small, but increase in size with the 

 growth of the inmate, and soon take an irregular course. The 

 larvae, when full grown, change to pupae, in a small cavity hollowed 

 out in the bark at the end of the burrow, and appear as perfect 

 insects in June or July, emerging from the tree by eating out a 

 circular hole from the pupal chambers. After the eggs are all laid 

 the female dies ; her dead body can be found at the end of the 

 chambers. The borings of the parents are not at first conspicuous, 

 but can be detected later by dust thrown out from between the 

 scales of bark, whereas the hole made by the exit of the beetles, 



