Walter Ritchie 339 



Then there is the additional injury of a technical nature done by the 

 larvae, namely, that caused through their tunnelling in the longitudinal 

 direction in the wood of the stem (Plates XXI and XXIi). 



In cases where stems are badly infested with larvae, the whole of the 

 wood may be completely riddled with such tunnels. As a result the 

 commercial value of the wood is rendered worthless. These injuries to 

 the wood by the larval burrowings do not alone directly cause the death 

 of the tree. The death is due principally to injuries of the bast and cam- 

 bium layers. 



Further, the making of exit holes by the larvae in preparation for the 

 issue of the imagoes, the widening of them by the imagoes, and conse- 

 quently, the allowance of air and moisture into the centre of the stems, 

 hasten still more the destruction of the wood. In many cases in which the 

 stems had survived an earlier attack, the flight holes had been completely 

 occluded through the growth of the outer bark layers and were completely 

 hidden to view. Where all the wood is practically destroyed, or the stem 

 sufficiently injured by the larval tunnels the tree is greatly weakened 

 against wind. Hence it is not an uncommon occurrence on the examina- 

 tion of an infested area after a wind storm, to find many of the badly 

 infested stems broken over at their bases. 



In the areas under observation the damage done to the natural growth 

 was very great, practically every tree from five to twenty-five years of 

 age showed signs of infection in one stage or another. Some of the trees 

 which had survived a bad infestation were still alive but showed a 

 stunted growth, their bases being much swollen and bearing deep black 

 fissures. Others had quite hollow stems, the wood in their centre having 

 been completely destroyed (Plate XXIII). 



It is evident then, that if artificial plantations or nurseries containing 

 poplars were in the neighbourhood of areas where the natural growth 

 was badly infested, the trees present in them would be greatly endangered 

 and considerable loss would ensue from an attack. 



Evidences of Attack. 



The first indication that adults are present in any area of poplars 

 may be known by examination of the leaves and stems of the trees. 

 Should adults be present, holes on the leaves — the boundary of the 

 wound showing serrations — will be found. This evidence of the presence 

 of beetles is easily recognised once attention has been drawn to it, and 

 I make special mention of this as at this stage the beetles could be looked 

 for and collected before egg-laying had commenced or been completed. 



