SIREX GIGAS AND SIREX JUVENCUS IN BUTE AND ARRAN. 305 



Occurrence of Si rex gigas, Linn., and Si rex juvencus, 

 Linn., in Bute and Arran. 



By John Ballantyne, Hamilton. 



[Read 28th January, 1902.] 



Some four years ago I brought under your notice the occurrence 

 of Sirex gigas in Bute and Arran, a number of the females of 

 which had been obtained. At that time the specimens had all 

 been secured from Scotch fir, but since then I have collected 

 a large number from silver fir, and also males of a very small 

 size from larch. Specimens of the latter were submitted to 

 Mr. H. P. Grimshaw, Edinburgh, who states they are the 

 smallest form of the insect he has seen, some of them measur- 

 ing about half-an-inch in length, and others a little more. One 

 female and one pupa of average size were also obtained from 

 the larch, but all the larvae were considerably smaller than 

 those from Scotch and silver fir. I am not able to give any 

 explanation as to the smaller size of the insects — especially the 

 males — from larch, unless there is something in the nature of 

 the wood to account for it. Specimens of larvae, pupae, and 

 perfect insects are here for inspection, and also pupa sheaths. 

 With regard to the latter, they must be looked for amongst 

 the borings left in the passage through the wood where the 

 larvae underwent the pupal state. When the larva is ready 

 to enter this state, through some natural instinct it makes for 

 the outside of the wood, and generally ceases boring about 

 three-eighths of an inch from the surface, or immediately under- 

 neath the bark, where it enters into the pupal stage of its 

 existence. When ready to emerge, the sheath is thrown off, 

 and the perfect insect cuts through the remaining part of the 

 wood, and emerges through a slightly smaller hole than that 

 occupied by the larva, as will be observed from the pieces of 

 wood exhibited 



