THE GENUS DENDBOCTONUS. 31 



bark and thus destroy the broods; (e) by transporting the infested 

 trunks a sufficient distance (20 to 50 miles or more away) from the 

 forest and away from any hving spruce or pine, so that the beetles 

 emerging from them will find no trees to attack. 



ATTEMPTS AT COMPLETE EXTERMINATION OF THE BEETLES UNNECES- 

 SARY. 



As a rule, it is not only useless but unnecessary to attempt the 

 complete extermination of one or more species of the beetles within a 

 given forest. It is necessary, however, to so reduce and weaken their 

 forces that they can not continue an aggressive attack, thus leaving 

 them to depend upon weakened and felled trees for their support 

 and to occupy a defensive position against their natural enemies. 



It must be kept in mind that the beetles must occur in great num- 

 bers in order to be successful in their attack on healthy trees. If 

 their number is reduced and kept below that required for kilhng 

 trees they can do no harm. Therefore in the case of a destructive 

 outbreak it is necessary to destroy only from 50 to 75 per cent of 

 the beetles in order to bring them under complete control. 



REQUISITES FOR SUCCESSFUL CONTROL. 



The principal requisites for success in deahng with these beetles 

 are: (a) Prompt recognition of evidences of their presence before 

 they have extended their depredations beyond a few scattering 

 clumps or patches of trees; (6) positive identification of the species 

 involved; (c) prompt action in adopting the proper method of con- 

 trol; and (d) rehance on expert advice relating to the essential features 

 in the habits and seasonal history of the insects, on which the action 

 is based. 



HOW TO CHECK AND CONTROL AN EXTENSIVE INVASION. 



If the depredations by species 9, 10, 13, 14, or 15 have spread over 

 a large area and there is yet a large amount of living timber or adja- 

 cent healthy forests to be protected, a careful survey should be made 

 in September, October, or November, for the purpose of locating the 

 areas and locaHties of new infestation in which the trees were attacked 

 during the summer and fall and which, at the time of survey, 

 contain living broods. The areas of principal infestation and the 

 larger patches of infested trees should be designated on a map, and 

 estimates made of the total amount or percentage of timber affected. 

 This will form a basis for definite plans and the organization and 

 equipment of a sufficient force to do the required work within the 

 specified time designated for each species. Then, if regular logging 



