330 



The Large Poplar Longhorn 



downwards, it gnaws gradually deeper and deeper into the sapwood 

 until finally the centre of the stem is reached. On the root portion of 

 the tree being reached the larva turns about and tunnels up the centre 

 of the stem. This part, at the turning point, is much widened and is 

 irregular in outline. 



—b 



Fig. 23. Fig. 24. 



Fig. 23. Typical form of larval gallery on a 7 year old poplar stem. (The horizontal scale 

 to which figure is drawn is much greater than the vertical.) a = horizontal or initial 

 portion of gallery on outer layers of sapwood; 6= vertical portion of gallery in wood; 

 c=exit hole; d = pupal portion. 



Fig. 24. Another form of larval gallery. Larva here after having tunnelled for some 

 distance downwards proceeded and tunnelled upwards. a= horizontal portion of 

 gallery on outer layer of sapwood; 6 = portion of gallery in wood; c = exit portion of 

 gallery; d = pupa] chamber. 



(c) The radial or exit portion. 



On its way up the centre of the stem tbe larva turns round and bores 

 in the transverse direction, cutting through the sapwood and bast, and 

 ultimately reaching the outside of the stem (see also Fig. 25). This portion 

 of the gallery is regular in outline and is elliptical in section, its greatest 

 breadth being in the vertical direction. In some cases, however, the exit 



