230 
MR WALTER RITCHIE ON THE STRUCTURE, BIONOMICS, AND 
being continuously weakened and predisposed to the attack of other enemies. The 
most damage is caused by the beetles feeding in the young shoots of pines in order to 
ripen their reproductive organs or for recuperation after egg-laying. The result of 
this tunnelling in the shoots of healthy trees leads to great loss of foliage, as the 
tunnelled shoots are broken off by the wind. There are two main attacks on the 
shoots, the first by newly escaped beetles, which have to feed in order to develop 
their reproductive organs before egg-laying, and the second, by the beetles which 
have paired and laid eggs, and which previous to a second egg-laying renew their 
feeding in the shoots. The former takes place from mid August onwards, the latter 
from late June onwards. The damage by these attacks greatly reduces the vitality 
of the trees, and the weakening of the trees prepares their stems for successful attack 
by this beetle for brood purposes. 
The characteristic shape of the crown of the pine becomes quite altered by the 
blow-down of the tunnelled young shoots, so that it becomes like, and mimics the 
form of spruce. Such damage and such misshapen trees are commonest at the 
edges and exposed parts of the wood, but are not altogether confined to these parts. 
Trees here and there in the middle of the wood show the same damage, and gaps 
are visible to the eye. The result is not only a direct loss to the tree, but an 
indirect loss to the forest owing to soil deterioration by opening the way for light. 
There is considerable loss in wood increment also from the loss of shoots and 
foliage. 
Then there is the damage done by the mother and larval galleries. The mother 
galleries of minor run in the transverse direction, and sometimes quite encircle the 
young stem ; in thicker places such galleries link up with others, and as a result the 
passage of sap is interfered with. Small dry dead patches of bark are found here and 
there on the stem as the result of minor attack. In the case of piniperda large sheets 
of bark covering the place of attack can be pulled away easily. 
It is of great importance to the forester to know where M. minor breeds, inasmuch 
as it is while breeding that this species can be most successfully attacked and its 
numbers reduced. M. minor breeds on standing Scots pine trees from thirty to fifty 
years of age. It may also use the smaller side branches in the crown. As far as I 
have found, the beetle prefers standing trees : only in one case have I found M. 
minor breeding on a felled Scots pine stem. While this is my experience over a 
considerably large area examined in Aberdeenshire, it is quite possible that in different 
conditions M. minor may use more freely than I have found it to do so, felled or 
blown stems for brood purposes : for example, Borodaewskij * states that in the 
State forests of the province of Minsk (Russia) M. minor breeds very frequently on 
felled trees, even preferring them to standing ones. 
In plantations of Scots pine where M. minor was very prevalent I arranged felled 
trees as traps in April 1916. These were thin-barked stems of about thirty years old, 
* Borodaewskij, P., in Liesnoj Journal ( Forestry Review ), year xlv, part 8-9, pp. 1222-1247, Petrograd, 1915. 
