25 



lodgepole pine caused by the Western White Pine Bark-beetle. In parts of the 

 infested country the trouble commenced nearly twelve years ago, and practically 

 all the pines have been killed (P. 6, figs. 2, 3, 4). Injury to the mountain balsam 

 by the Destructive Western Balsam Bark-beetle, Dryoccetes confusus Sw., is 

 sporadic in many localities over a wide area between Lesser Slave lake and the 

 main hne of the Canadian Pacific railway through the Rockies and Selkirks, 

 but in certain districts it may be considered epidemic. 



Conditions Favouring Bark-beetle Outbreaks. 



In addition to the weather, latitude and altitude, there are various local 

 conditions which favour the rapid development of the beetles, and, therefore, 

 are directly concerned in the origin of sporadic and epidemic outbreaks. 



SLASH. 



The refuse from cutting operations, culls, branches, tops, and stumps 

 affords an ideal breeding-ground for practically all our injurious bark-beetles 

 as well as for many other injurious species. Logging operations, settlers' 

 clearings, and even cuttings for firewood and for trail-making, provide slash that 

 may prove a positive menace to the surrounding health}^ timber. 



In order to control our destructive bark-beetles it is only necessary to 

 reduce the numbers so that the normal amount of dying bark to be found in 

 the woods will suffice for breeding purposes. Apparently all our bark-beetles 

 have, normally, a preference for dying bark; and it is only when their numbers 

 are very great that green timber is attacked in quantity. It therefore follows 

 that so long as extensive cutting in a district continues, the slash and stumps 

 serve as a breeding-place, and to a considerable extent, or for a time often 

 entirely, protect the healthy trees from most species of beetles. Broods of our 

 most injurious species which have bred in an epidemic outbreak in green trees 

 have apparently a decided tendenc}^ towards green timber. Unless the amount 

 of slash increases from year to 3'ear, certain species are bound to develop to 

 such numbers that additional breeding-places are required, and then, or, with 

 certain species, apparently before that stage is reached, they attack the sur- 

 rounding green timber. When cutting ceases suddenly there is always danger 

 that an outbreak may develop in the neighbourhood. 



It is therefore evident that while slash may serve for a longer or shorter 

 time as a partial protection to the standing timber, it is likelj^ to become a 

 nuisance, since it offers an abundant food supply for the beetles in which they 

 may breed to immense numbers. 



The slash can be made to serve as an effective trap. Many injurious 

 species will pass the winter chiefly as young adults or larvse in the bark. If 

 the slash of the previous summer's cutting, is burned during winter and early 

 spring, a sufficient number of the beetles will usually be killed to hold the injurious 

 species in check. When there is but one brood each season, as with the Mountain 

 Pine Bark-beetle, winter burning of slash of the previous winter's cut will be 

 effective. When species with two broods are involved summer slash burning 

 in early August, of the previous winter's cut, would assist in their control. The 

 most important consideration, however, is the destruction of the slash by fire 

 before the beetles can breed in it and emerge to infest nearby timber. Properly 

 conducted slash burning will be exceedingly effective in averting injuries by 

 both forest insects and fungi. 



GROUND FIRES. 



Light burns also provide an abundant supply of dying bark for breeding 

 purposes. The injured and slightly burned trees are in some cases as dangerous 



