102 



Wood Wasps. 



[may. 



forest and suppressed trees are selected by the steel-blue 

 wood wasp, and also trees 70 years old and upwards. The 

 giant wood wasp larvae have been found 4 in stems from 

 40 to 50 up to 120 years of age. In cases where the insects 

 are abundant the branches as well as the main stem are used 

 for egg-laying. 



Preference in egg-laying is for sickly suppressed trees and for 

 those in any way wounded or injured, trees that have been 

 barked in places, and trees already weakened by the attack of 

 other insects. Perfectly sound stems that have been felled and 

 are left lying are willingly made use of as brood places. Wood 

 wasps do not lay in rotten wood. While Sirex attack may 

 hasten the death of a tree already suffering from the invasion 

 of other insects, the chief harm done is by rendering the wood 

 useless for technical purposes. From a piece of old Scots 

 pine stem 10 ft. long, I bred out over forty Sirex juvencus ; 

 from an Austrian pine cut into logs more than 100 larvae 

 and adults of Sirex juvencus were taken. Where infestation 

 is so bad, it is easy to understand that the wood left may be 

 fit only for the fire. 



Preventive Measures. — j. The removal of any suppressed and 

 sickly standing trees which if allowed to remain would provide 

 suitable places for egg-laying and development. 



2. The timely removal of broken, blown or felled timber, 

 which would also be favourite places for egg-laying. 



3. The burning of badly infested stems as a preventive 

 against later and worse damage. 



4. If it were known that cut or prepared timber was 

 infested and that no great development of the larvae had 

 taken place, the owner might consider whether it was 

 worth his while to prevent further destruction by impreg- 

 nation. 



5. The larvae of an ichneumon (Rhyssa persuasoria) devour 

 the wood wasps' grubs. The Rhyssa is a large and handsome 

 insect with an ovipositor of great length and serrated at the tip. 

 By means of the long ovipositor, Rhyssa bores into the infested 

 stem and lays an egg in the gallery of the Sirex larva. The 

 Rhyssa maggot on hatching feeds on the wood wasp grub. I 

 have had Rhyssa persuasoria sent to me for determination 

 from Glamorgan, Aberdeen, and Arran. 



