768 



probably because they were too few. The beetles are very seldom 

 killed by the resin. During a serious attack about 300 holes per 

 square metre are present, the tree or part of it being then killed. When 

 the beetles are less numerous, they seem instinctively to avoid spreading 

 over the whole tree and only attack part of it. The part chosen seems 

 generally to be the southern or south-western side, the area being very 

 elongated ; the larger the tree, the larger the area. The cambium is 

 destroyed and the external layer of the wood is dead and usually 

 attacked by the fungus, Ceratostoma piliferuni. The areas attacked 

 were found at different heights on the trees, sometimes low down 

 sometimes in the crown. As a rule, trees from 9 to 11 inches in 

 diameter at about 5 feet from the ground, were preferred. The beetles 

 attack the whole trunk, except near the base and at the top. The 

 attack was never begun by Ips chalcographus at the top, this species 

 always following the attack of /. typographus. It probably depends on 

 climatic conditions how high up the attack takes place in the 

 tree, the beetles flying higher during warm weather ; this accounts 

 for the fact that felled trap-trees are not often attacked, although 

 growing trees in the vicinity are killed. The trees injured by the bark- 

 beetles are generally attacked by the fungus, C. piliferuni, which reduces 

 the value of the timber. In order to prevent this, it is necessary to 

 cut the attacked trees as soon as the larvae begin to develop, which" 

 at Orsa takes place in the beginning of June or later. As the develop- 

 ment of the brood may be completed in six or eight weeks, and the 

 attack may begin in May, the trees first attacked must be cut and the 

 bark removed at the end of June, or earlier in the southern part of 

 the country. In Orsa, the amount of timber destroyed by the bark- 

 beetles in 191-4 was approximately estimated at 70,000 cubic metres. 

 The decrease in value caused by the fungus was about £3,850 and in 

 the whole country the losses due to the bark-beetle amounted to some 

 millions. 



The best method of controlling the beetles is to remove the bark 

 from the trunks attacked. Partial barking is not sufficient, as many 

 beetles succeed in undergoing their transformation in the pieces of 

 bark left, especially in dark and damp places. Partial barking does 

 not affect /. chalcographus at all. The trees must therefore be barked 

 so early in the year that the larval galleries are not more than 1 cm. 

 long. In the middle of May, if the climatic conditions are favourable, 

 the beetles may be found on the trunks ; all the attacked trees must 

 then be marked, and their diameter measured, so that all can be felled 

 and barked in proper time. New swarms arrive later and attack the 

 remaining trees, which must be watched, as well as the attacks higher 

 up on the trunks, which are more difficult to detect. Whenever the 

 attacked trees were cut and barked in good time, the result was most 

 satisfactory, and the trunks did not suffer if they were stored in shady 

 places. The beetles often leave localities where the conditions seem 

 quite suitable, and in many of these cases the larvae appear to suffer 

 from some disease. 



