The Problem of the Bark Beetle 91 



possible to kill off ^lu-h a large proportion of thoir nuiiiliers liv rnoiliticatioiis of the logging 

 nietho'ls that the roniainiler will lie largely sati>fieil to hreeil in the ^lash anil broken trees 

 without attacking the green timber. 



The appearance and habits of the various species, while differing often in very im- 

 portant details have many points in common. The more injurious species are small, ^tout, 

 usually reddish-brown or pitch-coloured beetles with hard wing-covers, varying in length 

 from less than one-eighth to about one-third of an inch. The young are small, legless, 

 whitish grubs with powerful jaws, found working in the inner bark or between the l)ark 

 and the wood of the infesteil trunks. 



The winter is usually passed by the adult beetles and their grubs in or beneath the 

 bark of trees attacked the jireceding summer, in the late spring or early summer the mature 

 beetles leave the old bark and enter the bark of the trunks and branches of disease"!, dying, 

 or healthy trees in immense nundiers. We have found as many as :i,(i(iO ])airs of beetles 

 entering the lower fifty feet of the trunk of an infested yellow pine. Kach pair of beetles 

 cut an entrance-tunnel through the bark to the surface of the wood and continue this as an 

 egg-tunnel along the wood-surface, scoring both inner bark and sap-wood. These egg- 

 tunnels may be vertical, transverse or irregularly winding. The effect, in any case, .when 

 green timber is entered, is to check the sap flow in jiroportion to the number of beetles 

 uniting in the attack upon the tree. In the ease of green pine and spruce, the cutting of 

 the entrance tunnels and egg-tunnels always results in a flow of resin which hardens about 

 the entrance-hole and drops on the bark below as masses of gum. These gum-tubes on the 

 bark of green trees usually indicate an attack of destructive beetles and should lead always 

 to a dose investigation. The female beetle deposits her eggs in elongate masi^es, or in 

 niches, along the sides of the egg-tunnel. The grubs hatch in a week or so and bore singly 

 or in congress in the inner layers of bark or usually between the bark and wood. These 

 larval mines when regular, as they are in many species, form rather handsome bits of 

 carving; but whether regular or irregular they very effectively destroy the inner bark and 

 stop the flow of sap through the portion attacked. If they entirely girdle the tree, the latter 

 dies in a few months, usually becoming yellow before spring and a ''red-top" by the fol- 

 lowing July. The grubs mature to the adult beetles in the ends of their mines, either be- 

 tween the bark and the wood or, more rarely, deep within the middle layers of the bark. 

 Early in the following season the young beetles leave the infested trees, then "red-tops," 

 anil attack fresh trees. With some species the old beetles also emerge very early and pro- 

 duce another brood. With many species there is, as indicated in the outline just given, but 

 one brood each season, or one and a partial second brood, through some of the young beetles 

 emerging in the fall; but other species have regularly two broods each summer. The varia- 

 tions in climatic conditions have a marked influence upon the rapidity of development. 



All our British Columbia species normally prefer weakened or dying trees or slash for 

 breeding purposes; but the more destructive species will readily attack and kill healthy 

 timber when they have had opportunity to breed to immense numbers. 



SLASH BURNING AS A EEMEDY. 



In the brief account of their general habits just given we have suggested two im- 

 jiortant methods of control. The less destructive species, such as the Douglas Fir Beetle 

 and the Sitka Spruce Beetle, with their strong preference for dying bark, will breed for a 

 considerable time in the sla-sh while the cutting continues; and nearly all the beetles of the 

 neighbourhood of the species involved will he found in the Vjark of the summer's or previous 

 winter's slash during the winter. It is therefore evident that if the slash is burned at any 

 time between November and May the vast majority of the broods will be destroyed. Those 

 that escape will usually find abundant breeding material in the normal crop of sla.=h and 

 broken or injured trees. Systematically burning the slash during the time between fall 

 and spring is a very efficient method of control for most of our bark-beetle species. 



The second method has reference to the control of outbreaks in standing timber. 

 Inasmuch as the beetles are to be found, in this case, during the fall, winter and spring, 

 in the bark of the trees attacked the previous summer, it is evident that if we can log the 

 majority of those infested trees during that period and so handle the logs as to destroy the 

 broods contained in the bark, we can hope to reduce the numbers of the beetles to such a 

 degree that they will thenceforth find sufficient breeding material in slash and not molest 

 the green standing timl>er. K.\tensive control operations carried on in the Western States 

 by the U. S. Bureau of f^ntomology have demonstrated that if 75 per cent, or even a lesser 

 percentage of the infested trees can be so removed and treated the outbreak can be effec- 

 tively checked. 



'When it becomes necessary to undertake direct control measures, the broods in the bark 

 of the infested trees can be destroyed Ijy whichever of the following methods are best suited 

 to local conditions: 



