176 JOUENAL OF THE ROYAL HORTICULTURAL SOCIETY. 



or hydrocarbons, which will enable them to spread over the 

 surface of the plant on which they are sprayed. For these 

 insects arsenic should not be used. 



There are many insects which take possession of the dead or 

 dying tree to lay their eggs therein whose larvae burrow into and 

 penetrate the wood, making it useless for commercial purposes. 



Of these the most important are the wood-wasps, Sirex 

 gigas and juvencus, large Hymenoptera of elongate shape. 

 S. gigas is yellow-and-black, and of a decided wasp-like appear- 

 ance, while S. juvencus is deep blue, with the middle segments 

 of the abdomen reddish in the male. 



Wood-wasps. 



These insects appear to be somewhat widely distributed in 

 Great Britain and Ireland, and are occasionally not rare. To 

 judge, however, from the way in which entomologists think it 

 desirable to record the specimens which come under their notice, 

 they can hardly be described as generally common. Owing 

 to their striking appearance and loud buzz in flight, they attract 

 general attention, and are probably as rarely overlooked as any 

 indigenous insects. Not a few recorded specimens are obviously 

 imported in foreign timber. The females of both species lay their 

 eggs on Conifer-wood exclusively, choosing, as is so often the 

 case, sickly or dying trees, or those that are actually felled or 

 dead. Snex gigas appears to attack principally the Spruce and 

 Silver Fir, sometimes the Larch and non-European Conifers like 

 the Deodara. 



According to German observers, it does not touch the Scotch 

 Pine, and I have seen no English statements to contradict this. 

 Unfortunately, it is often impossible to make out exactly what 

 species of Conifer is referred to by English entomologists. 



Sirex juvencus, on the other hand, attacks the Scotch Pine 

 freely, as well as the Spruce, Silver Fir, and Larch. 



The eggs are deposited in cracks running through the bark 

 into the sapwood, or in holes made by the strong ovipositor, and 

 not rarely on patches of bare wood where the bark has been torn 

 off by accident. This sometimes gives an opportunity for injury 

 to otherwise healthy trees. The larva, whose life extends over 

 two years, is a stout, elongate white grub, readily distinguished 

 by an upwardly directed point on the last segment ; it bores 



