4e Canadiari Arctic Expedition, 1913-18 
In his field notes Mr. Johansen says of these tunnels: " The oripjin 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 
Pohjgraph'us and PiMjoyhthorus 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 ahve, 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 Xijlotrechus 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 larva?, indicated that the parasites were exerting 
effective control. 
Several sawfly larvae were using these wood tunnels as a winter retreat. 
They are discussed elsewhere in the reports of this expedition. 
The smaller wood tunnels just referred to were cut by Neoclytus muricatulus 
Ky. One dead adult of this species was removed from a tunnel below the wood 
surface after the matetial 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, p'-actically the northern limit of trees 
on the Coppermine river. He considers that those insects had killed the majority 
of the numerous dead trees he saw in that locality; and 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. 
