1928 



Canadian Forestry Journal, November, 1918 



A New Forest Insect Enemy of the 

 White Birch 



By J. AI. SwAiNi: 

 Chief, Division of Forest Insects, Entomological Brancli, Lttawa 



A new and highly destructive 

 enemy of the white birch was dis- 

 covered by us this summer in Quebec 

 Province, and serious injury from 

 probably the same cause has just 

 been reported from another locahty. 



In the region examined by us the 

 disease was evidenced by many dead 

 white birches, visible in every direc- 

 tion, indicating that the outbreak 

 had been in progress for at least 

 several years. Of the living trees 

 probably over 50% are already badly 

 diseased, and show the characteristic 

 d>dng branches in the upper part of 

 the crown. 



Nature of the Injury. 



The injury is caused by a small 

 bronze-black beetle, known as the 

 Bronze Birch Borer, Agrilus anxius. 

 The eggs are laid in the bark during 

 June and July. The larvae or grubs 

 excavate long winding tunnels through 

 the inner bark and sap wood of both 

 branches and trunk, and since the 

 mines are frequently very numerous, 

 the sap-flow is checked and the 

 affected portion of the tree may 

 succumb very rapidly. The winter 

 is passed in the larval stage in cells 

 situated in the outer part of the sap- 

 wood, and the adult beetles, having 

 developed from the larvae during 

 the following spring, bore half-round 

 holes through the bark and leave the 

 tree chiefly during June and July. 



Injured living trees show dying 

 upper branches; when these dead or 

 dying limbs are peeled, the charac- 

 teristic winding tunnels of the larvae 

 on the surface of the sapwood often 

 form a tangled network. 



Flxtent of the Injury. 



We do not yet know how widely 

 the injury is distributed through out 

 the Province, but it is ])robably of 

 more than local importance. It ap- 

 pears to be spreading rapidly in the 

 section examined: about 50% of the 

 white birches arc ])adly injured and 



the remaining healthy trees will 

 apparently be attacked within the 

 next few years. 



The Bronze Birch Borer has long 

 been known as the most serious 



enemy of cultivated birches in the 

 Ottawa Valley and other parts of 

 Eastern America; but, although we 

 have found it breeding in small num- 

 bers in wild birches, this is the first in- 

 stance known to us where it has 

 developed into a really serious forest 

 pest. It is interesting that an enemy 



