256 Proceedings of Eoyal Society of Edinburgh. [sess. 1 
Another peculiarity in the galleries made by the parent insect in 
the larch, is that in a large number which I have examined I have 
only on one occasion found an air-hole. This is somewhat remarkable, 
because, when the galleries are made in the natural food-plant of 
the insect, at least one air-hole is present in each, and, as a general 
rule, they contain two or three. I am somewhat at a loss to account 
for this, because, half-smothered by resin as the insects are in their 
galleries, the admission of air would appear to be a most desirable 
consideration. It is probable that here also the great amount of 
resin in the cortex of the larch interferes with the normal formation 
of the galleries. 
As to the cause of H. piniperda attacking the larch, I believe 
a ' satisfactory reason can be given. About ten years ago the 
southern counties of Scotland were visited by a succession of ex- , 
ceptionally severe gales, which overturned enormous numbers of 
pines and other trees. Partly owing to the glutted state of the 
market, and partly to the difficulty experienced in dealing with 
such a large amount of fallen timber, the woods were allowed to 
remain undisturbed in their devastated condition for a number of 
years. These dead and dying trees furnished an exceptionally 
favourable breeding-place for H. piniperda , which consequently 
increased at a prodigious rate, each average-sized pine being capable 
of producing, it is said, as many as 80,000 insects. Within the 
past year or two the last of this fallen timber has been removed, 
with the result that the huge army of forest insects, by which the 
country is overrun, cannot be accommodated with the breeding- j 
places which they prefer, and have therefore been compelled to 
oviposit on what they must consider most unsuitable material. 
Thus, owing to stress of circumstances, H. piniperda has been 
driven to attack the larch, and in this country I have also found 
Scots pines, not exceeding eight years of age, infested by it, although 
hitherto trees of a less age than fifteen years have seldom been 
known to be attacked. 
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