4 k Canadian Arctic Expedition, 1913-18 



In his field notes Mr. .Johansen says of these tunnels: " The origin of this 

 burrow could always be traced to a wound .on the tree, a branch broken off 

 by storms, a fire wound, or bare patch on which the bark had been killed by 

 bark-beetles." 



Many of the living trees were examined by Mr. Johansen, and although 

 the young trees and those growing in a close stand were but little affected by 

 insects, numbers of the others had dead and dying parts attacked by bark- 

 beetles or cerambycid grubs. 



Dendroctonus was not found at all in these living trees and the tunnels of 

 Polygraphus and Pityophthofus were less numerous than in the dead timber 

 just described. The cerambycid larvae appeared to be more destructive. Trees 

 were found with the top dead and the base sound, with fresh cerambycid tunnels 

 in the area between the dead and the healthy wood and extending down into 

 the latter. Many of these tunnels were apparently confined to the inner bark 

 and surface of the wood, while others were started on the wood surface and 

 extended deep into the wood itself. 



From the surface tunnels six larvae were taken, varying in length from 

 6 mm. to 20 mm. These were kept frozen for eventual rearing; but when 

 thawed out in May, 1916, only two (10 mm. and 15 mm. long) were alive, and 

 these died later before transforming. Dead adults of Merium proteus Ky. 

 were found in pupal cells at the ends of these surface tunnels, or in exit tunnels 

 leading from them, so that this species was apparently responsible. Many 

 empty hymenopterous cocoons were found in these tunnels beneath the bark. 

 Mr. Johansen says: " often I would find, instead of the cerambycid larva and 

 adjacent to the larval skin, the cocoon of the parasitic hymenopter; these cocoons 

 were empty or contained dead pupae, excepting one which held a living larva." 



The tunnels extending into the wood were of two sizes and doubtless made 

 by distinct species. The larger of the two was like those in the dead trees 

 already described from which adults of Xylotrechus undulatus Say were taken. 

 Only two living larvae of this wood borer were found; these were lying frozen 

 stiff in the inner ends of the burrows. These Xylotrechus tunnels always 

 originated at a wound or other exposed surface. They lie on the outer surface 

 for a short distance and are there filled with boring dust, but extend later 

 deep into the wood, eventually becoming longitudinal; there was practically 

 no boring dust in the part of these uncompleted tunnels lying below the wood 

 surface. This species was also heavily parasitized. In the ends of the larval 

 galleries Mr. Johansen often found, instead of the beetle larva, an empty cocoon 

 of a hymenopterous parasite, and the large number of these, together with 

 the scarcity of the cerambycid larvae, indicated thit the parasites were exerting 

 effective control. 



Several saw fly larva? were using these wood tunnels as a winter ret rent. 

 They are discussed elsewhere in the reports of tins expedition. 



The smaller wood tunnels just referred to were cut by Neoclyty,s muricatulus 

 Ky. One dead adult of this species was removed from a tunnel below the wood 

 surface after the material reached our laboratory. These tunnels, in so far as 

 represented in the collection, are on a dead stub projecting from a branch still 

 living when it was collected, but containing tunnels of the Xylotrechus. 



In closing his field notes Mr. Johansen states that forest insects, including 

 bark-beetles and cerambycid larvae, have caused serious and extensive injury 

 to the white spruce, even in that region, practically the northern limit of trees 

 on the Coppermine river. He considers that those i Lse< I had killed the majority 

 of the numerous dead trees he saw in that locality: ana! he suggests that the 

 injuries to the most northern trees previously ascribed by Richardson and 

 others to fires and unfavourable climatic conditions may have been really 

 caused by similar insect outbreaks. 



