106 PROTECTIOF^ OF PLANTS — 1923-24 



however, will be met when the larva visits the mouth of the tunnel, previous 

 to pupation (as it were to insure that everything is in readiness) and should 

 the passage be blocked it will cut away obstructions and remove all debris, 

 leaving a clear exit for the spined pupa, later to wriggle its way through to 

 freedom. This natural provision while not peculiar to P. macmurtrei is note 

 worthy when it is considered that the adult is without mouth parts and helpless 

 to liberate itself in the event of meeting any serious obstruction. During the 

 summer of 1920 two instances of this nature were recorded. It was noticed that 

 the entrance of these particular tunnels had become blocked from the exterior 

 by the natural growth of another tree which had intersected with the host just 

 at the point of entrance. The character of the frass being expelled from narrow 

 slits led to the belief that pupation was to occur soon. Both exit holes were 

 watched with particular interest. One morning soon after the borings had 

 ceased each tunnel entrance was found freshly enlarged, the exterior rims 

 being gouged away clearly as if cut by a sharp penknife and made wide enough 

 to introduce the point of a little finger. This operation took placs at night, or 

 early in the morning, and was not witnessed. In due time both pupal eases 

 appeared and the adults were able to free themselves. 



It is not an uncommon occurance for larvae to leave their burrows and 

 wander about on the outside, even away from their host. They were observed 

 to do this quite frequently. On one occasion a large grub was found upon the 

 trunk of a white pine about 6 feet up. This nomadic habit which affects both 

 the old and young borers is strange when it is considered that their natural 

 habitat is within the narrow darkened galleries of the tree. 



Infested trees often become a good base for further larval operations, 

 forming what are known as "brood trees". Numerous observations lead to the 

 conclusion that once the larvae have become established in a certain tree, some 

 of the following generations will keep to the same oak and use the tunnels 

 made by former occupants to carry on their boring operations deeper and 

 higher up into the heart-wood. Under such an attack the tree is liable to 

 become badly honeycombed and its Interior converted into a labyrinth of 

 scoty tunnels which cross and intersect in every direction. On the exterior the 

 tree will heal its wounds by forming thick, horny, bulging scars around the 

 large holes commonly seen on the trunks and which often contain sawdust, 

 frass, rotten wood and other debris. Such conditions offer favourable openings 

 for wood-rotting fungi, and it is not surprising that their spores find a fruitful 

 ground for support and ready propagation. 



Borings are often seen near the base of a tree. In cases where infestation 

 has taken place previouslj'^ in this region, the moth Is likely to deposit there 

 again. Usually the female being heavy bodied and clumsy, seems loath ta 

 move far from where she originally has emerged until rid of at least part of her 

 burden; she may crawl up the trunk then into the upper branches, or fl^^ to a 

 neighbouring trunk and deposit the remainder of her eggs. The bark at the 

 base is liable to be cracked, particularly in older trees, and show crevices somes 

 distance up the trunk. These offer good locations for oviposition and are readily 

 made use of, no part of the tree may be said to be free from attack, and even 

 the small branches one inch in diameter, have been found intersected with 

 larval burrows. In such, cases, girdling is apt to occur and the branch will 

 break off or become a staghead. The killing back of the upper branches is very 

 characteristic and quite common. Many of the trees have their symmetry 

 completely ruined by these unsightly dead branches and ugly, gnarled, scraggy 

 tips projecting from different parts of the foliage. The larvae also tunnel 



