114 The Ottawa Naturalist. [Dec. 



Woodpeckers destroy large numbers of the Bark-beetles, and 

 at times help considerably to check their ravages. 



The tunnels, especially of the Timber-beetles, are frequently 

 overrun with various species of mites. The eggs of these mites 

 hatch before the young beetles are ready for their flight, and in 

 this way young and adult mites are carried by the beetles 

 attached to their bodies to the new tunnels. At certain times 

 the declivity of the elytra of various species of Ips (Tomicus) 

 will be found covered with minute mites, and Pterocyclon mali 

 and P. fasciatum are frequently almost completely covered with 

 them upon emerging from their tunnels in the spring. Many 

 of these mites appear not to injure their hosts; but certain 

 species are very destructive, and breed in the larval galleries 

 or pupal cells upon the young of their hosts. 



Fungous diseases are sometimes very destructive to them. 

 All stages of the insects are frequently found, more particularlv 

 in wet weather, filled and covered with the white mycelium of 

 the fungus. In a felled pine log I noticed that hundreds of adult 

 Ips pini had died from this cause in less than two weeks. 



Friends of the Scolytidaz .- As these beetles feed mainly upon 

 dying and dead branches and trunks of trees, any cause which 

 tends to weaken or destroy the trees aids the Scolytids in supplv- 

 ing the proper food-plant. Heavy storms, forest fires, other 

 insects, and the destructive work of man, are perhaps the chief 

 of these. 



Economic Importance. Owing to the destructive habits of 

 many of its members, the family Scolytidae is of considerable 

 economic importance. The injury done by these beetles may 

 take two forms: living trees may be weakened and killed, and 

 standing and felled timber and sawn lumber may be rendered 

 useless for manv purposes by the tunnels of the beetles. 



But few Scolytids attack living, healthy trees, although 

 there are a few species which apparently choose only trees in 

 this condition. The majoritv of species attack onlv dving or 

 dead trees, and a few breed in dead wood onlv. Stumps, diseased 

 or dead branches, brush piles and recently-felled logs are their 

 favouri J e breeding places. Most species will not, as a rule, 

 molest living trees at all if rapidly-dying and recently-felled food- 

 plants are available, but if trees in this condition are not to be 

 had in sufficient quantity, many of these species will attack 

 perfectly healthy trees and prove very destructive. 



The injurv done by the species which attack healthy and 

 diseased trees is, in certain regions and at recurring intervals, 

 very considerable. The work of Dendroctomts frontalis in the 

 spruce and pine of West Virginia and the adjoining States, of 

 D. piceaperda in the spruce of the Northeast, and of P. ponderosa 



