124 



THE SCOLYTID BEETLES. 



the insect at any time. If the work be done during the period begin- 

 ning with the middle of October and ending with the middle of May, 

 say at or below an elevation of about 1,800 feet at latitude 45°, the 

 parent adults and developed broods of adults, together with the 

 immature broods, will be killed. The infested parts of the trunks may 

 be barked without felling the trees, or the trees may be felled for this 

 purpose and barked or utilized and the slabs burned, as in each case 

 may be more practicable or desirable. If the timber can not be 

 utilized for several years it will remain sound much longer if barked 

 and left standing than if felled. 



If, in the case of a moderate attack, the larger clumps or patches 

 of infested trees and the more accessible scattering ones in the worst 

 affected sections of a forest are barked, it should serve to bring the 

 insect under control the first year, but in the case of a very extensive 

 attack this may require several years. 



** , v 



Fig. 76.— Trees girdled by different methods: o, Hack-girdled; b, girdled to heartwood; c, hack- 

 girdled and peeled; d, hack and belt girdled. (Author's illustration.) 



It is not necessary that every infested tree should be barked or 

 utilized, but it is important that at least 75 per cent of such trees be 

 either barked or removed in regular logging operations, before the 

 broods have time to emerge. 



Whenever a large amount of timber is being killed, as in north- 

 western Maine in 1900, the regular logging operations should be con- 

 ducted in the principal infested areas, in order that the infested trees 

 may be cut and floated out of the forest before the broods have time 

 to emerge. The adoption of this method by the Berlin Mills Com- 

 pany in 1901 was evidently very successful in controlling the insect 

 in the region referred to in B ulletin 28 of this office. 



It may be practicable to bark newly infested trees in August and 

 September, but the principal work of barking, or removal, or utiliza- 



