26 



beetle breeding grounds as the slash, and this should be considered when the 

 burns are being logged. If the fire has occurred in the first half of the season 

 and has charred only the bark near the ground, the timber on a burn must be 

 cut during the first winter following the fire, or not later than the second winter, 

 if anything is to be saved from the grubs of the large wood-borers.* Since the 

 logs will contain these living grubs, even though cut the first winter after the 

 fire, they must be got into water or sawed before spring opens; and when the 

 latter is done the lumber should be dried as rapidly as possible. All green slash 

 and small dying trees on the burn should be piled and burned to prevent the 

 breeding of bark-beetles and other insects. Trees which have been thoroughly 

 charred from base to top may be disregarded in so far as beetle control is con- 

 cerned. Burns which were made late in the season are, of course, frequently 

 immune from beetle injury, although this is true to a smaller degree in British 

 Columbia than in Eastern Canada. 



OTHER FACTORS. 



Wind-falls, snow-breaks, and flood injuries provide more or less dying timber 

 for beetle breeding grounds each season, particularly in the mountain sections. 

 Whenever any extensive injury of this kind occurs in government parks or 

 reserves, or on valuable private holdings, it is desirable to have the dying timber 

 utilized or destroyed before it can give forth its crop of destructive beetles. 



Natural Control Factors. 



The influence of weather conditions upon the broods has already been 

 discussed. The other natural agencies operating to check the development of 

 the beetles in our forests are, parasites of various kinds, predacious insects, 

 birds and fungi. 



PARASITES. 



Small hymenopterous parasites deposit their eggs on the larvse or near 

 them in their tunnels, and the young parasites kill the beetle larvse by feeding 

 upon their body juices (PI. 19, fig. 2). The larger of these parasitic species 

 deposit their eggs through the thin bark overlying the larval mines in the tops 

 and branches; the minute species enter the egg-tunnels and lay their eggs often 

 in the egg-niches. They affect different species of bark-beetles in varying 

 degrees. The most destructive bark-beetles, breeding in heavy, thick-barked 

 timber, are but little affected by them. On the other hand, some species, such, 

 for instance, as Leperisinus aculeatus Say, are frequently very heavily parasitized, 

 and the minute round holes through which the adult parasites eventually emerge 

 from the bark are often thickly interspersed with the exit-holes of the beetles. 

 A few of our species are sometimes heavily parasitized by mites which breed in 

 the mines and destroy the larvae about the time of pupation. 



PREDATORS. 



Predacious beetles and their larvse are frequently abundant about and within 

 the egg-tunnels and mines, and feed upon the bark-beetle adults, their eggs, 

 and the larvse. 



The influence of parasites and predacious insects appears, on the whole, to 

 be of minor importance in controlling bark-beetles in our forests; although it is 

 possible that some of our secondary species, normally rather heavily parasitized, 

 might otherwise be of primary importance. 



*Except the largest timber of the Pacific Coast. 



