The Problem of the Sirex 



of an inch thick is left intact at the end of the 

 vestibule. There is no other defensive pre- 

 caution; no barricade, no heap of shavings. 

 In order to come out, the insect has only to 

 pierce an insignificant sheet of wood and then 

 the bark. 



The Nine-spotted Buprestis {Ptoshna 

 novemmaculata) behaves in the apricot-tree 

 precisely as the Bronze Buprestis does in the 

 poplar. Its larva bores the inside of the 

 trunk with very low-ceilinged galleries, 

 usually parallel with the axis; then, at a dis- 

 tance of an inch and a quarter or an inch and 

 a half from the surface, it suddenly makes 

 a sharp turn and proceeds in the direction of 

 the bark. It tunnels straight ahead, taking 

 the shortest road, instead of advancing by ir- 

 regular windings as at first. Moreover, a 

 sensitive intuition of coming events inspires 

 its chisel to alter the plan of work. The 

 perfect insect is a cylinder ; the grub, wide in 

 the thorax but slender elsewhere, is a strap, 

 a ribbon. The first, with its unyielding 

 cuirass, needs a cylindrical passage; the sec- 

 ond needs a very low tunnel, with a roof that 

 will give a purchase to the ambulatory nip- 

 ples of the back. The larva therefore 

 changes its manner of boring utterly : yester- 

 day, the gallery, suited to a wandering life 

 213 



