232 
MR WALTER RITCHIE ON THE STRUCTURE, BIONOMICS, AND 
A point worthy of consideration is to what extent fungi are encouraged through 
the destructive work of the beetles. If M. minor is present in numbers and attacks 
healthy standing trees, there is no doubt that the reduction of foliage, as well as the 
wounds caused by borings, reduce the vitality of the trees and' predispose them to 
fungus attack, while the wounds and exit holes serve as entrance-places for wound 
parasites. 
Symptoms of Attack of the Two Species. 
The large numbers of tunnelled young pine shoots lying on the ground, broken 
off by high winds from the tree-tops above, is quite sufficient evidence of the 
presence of this species in a wood. The tree-tops above, as a result of the loss 
of shoots, appear as if they had been pruned, and pruned badly, while a number 
of withered shoots may be still found hanging on the trees. 
The presence of beetles boring below the bark can be readily detected by the 
occurrence of bore meal thrown out at the entrance-holes of the mother galleries. 
During May and June this bore meal should be looked for on standing trees. Later 
this sawdust can be traced in streaks down the bark, and can even occur in little 
heaps either at the surface of the ground or on the bark scales. 
Although the foregoing observations on M. minor are confined to the Aboyne 
district of Aberdeenshire, where in some places the species occurs in very large 
numbers and equally as common as its congener M. piniperda, yet I believe the 
occurrence of M. minor is more widespread throughout Scotland than is generally 
supposed. Its so-called rarity is probably due to the fact that in appearance it is 
so similar to the much commoner M. piniperda. Further, the damage done by 
M. minor to the young shoots through its feeding habits is similar to that of 
M. piniperda, and so the misdeeds of the known piniperda are ascribed to the 
scarcely known minor. In the woods where observations were made, the damage 
to the shoots by M. minor was equal to, if not greater than, that by M. piniperda. 
While the two species damage the shoots in the same way, minor may be a worse 
enemy than piniperda, inasmuch as it asks for a better quality for rearing its brood, 
and attacks standing trees. It has been stated before that minor favours rather 
the upper thinner-barked parts for brood purposes, and this can be a reason 
for its comparative rarity on felled stems, since these favourite places, the thin- 
barked parts, dry quicker, and therefore cease to provide the better quality which 
minor asks. 
The study of the two species and their work is further interesting, as showing 
that closely similar and nearly related species may sometimes be more easily 
distinguished by their behaviour than by their external specific characters. 
Thus, while the trained entomologist, armed with a lens, would have little 
or no difficulty in determining the two species by examination, both to trained 
