
THALESSA, OR RHYSSA SP. 157 
grubs had infested and finally killed having gone too deep into the 
wood. When this latter happens the ichneumon fly is said to 
bore inthe direction of the outside of the tree for a certain 
period and if it does not reach it within this time it gives up 
and dies, probably from exhaustion. The other adults found 
had apparently drilled a hole through the bark and in some 
cases alittle way into the wood, by means of their saw-like 
Ovipositors, until they reached a larval gallery in which they 
probably laid their eggs, The larve developing from these 
eggs probably feed upon the Szrex larve as external parasites. 
Dead insects were numerous in the tree, their ovipositors and 
portions of their bodies being often found in holes in the bark, 
the former being fixed in the wood whilst the upper portion 
of the body protruded from the bark. From examinations I 
was able to make of numbers of these, Iam of opinion that it 
may be possible that the ichneumons die zz sztu after laying 
their last eggs either near or amongst the Szvex eggs or in the 
larval tunnels. It would also appear probable that instinct leads. 
the Thalessa to lay its eggin the right place by enabling 
it to unerringly know where the larval tunnels and larve in 
the wood are. Without such knowledge it would seem impos- 
sible for the parasite, whose ovipositor is only 13 inches in 
length, whilst the spruce bark is often over an inch in thickness, 
to reach the larval tunnels. I think this latter is very probably 
the cas2 since the number of insects found in this position was 
considerable, 
Locality from where reported. 
This insect was found in the same locality.as already given 
for Szvex sp. 
Relations to the Forest. 
This ichneumon is evidently of some utility since it helps to 
keep down the numbers of so serious atimber-boring pest as the 
Stvex, It does not prevent the damage being done to the actual 
tree in which it is found since it is probable that the larve 
reach a considerable size, or, in other words, do a very consider- 
able amount of damage, before they succumb to the attacks of 
the ichneumon grubs, At the same time it does a small amount 
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