Walter Ritchie 



331 



hole appears only as a longitudinal crack on the surface of the bark. 

 Usually the exit hole occurs about four to six inches above the level of 

 the ground but in a few cases it was cut well up the stem, occurring as 

 high as one and a half feet. As a rule this portion of the gallery is not 

 completed all at once, but the larva returns again and again from the 

 centre of the stem until it is completed. On the completion of this portion 

 of the gallery the larva plugs it tightly with gnawed material. 



(d) The pwpal portion. 



The larva now continues to bore up the centre of the stem in the 

 vertical direction and may reach a height of 1 ft. 9 in. or 2 ft. in the 

 centre of the stem. By this time it is full grown and is ready for pupation. 

 Enlarging slightly the diameter of the portion of the tunnel just cut, 



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Fig. 25 a. Portion of stem of a 12 year old poplar showing oval exit hole made by larva 



for exit of adult. 

 Fig. 25 b. The same in transverse section to show the complete exit portion of gallery. 



i.e. the uppermost portion, it seals the burrow tightly behind it with a 

 dense plug of coarse frass ripped roughly from the side of the gallery. 

 This operation being completed, the larva now within its pupal bed, 

 ceases to feed, reverses its position, its head-end resting on the plug of 

 frass at the lower end of the cell, shrinks slightly, moults, and the 

 pupa is revealed. The moulted chitinous head parts of the larva are 

 found lying in the upper end of the pupal chamber. The length of the 

 pupal chamber is on an average 1-| inches. 



The time taken by the larva for the completion of the whole gallery, 

 excluding the hibernating period, is about eight and a half months. 



After the period of pupation has passed, the young imago bores 

 through the plug of frass at the base of the pupal chamber, and then 



