366 



Insects most injurious to Cultivators : — 



had invariably gnawed a channel at the base of the young 

 shoots of last year, sometimes almost entirely round. This, of 

 course, entirely prevented the flow of sap, as well as so much 

 weakened the stem, that a little wind was sufficient to make 

 them fall. M. V. Audouin considered that these insects (whose 

 habit it is to burrow under the bark of the common oak) had 

 made their escape from the great chantiers de bois a bruler, 

 on the adjacent banks of the Seine, having been carried there 

 in the logs of fire-wood, whence they had flown into the Jardin 

 des Plantes, and had there discovered this species of oak, the 

 wood of which was so hard, that they had relinquished their 

 ordinary habits, and had attacked the base of the young shoots 

 for food. This seemed to be the natural explanation of the fact, 

 because we found only two or three of the insects in burrows in 

 the trunk, in which they had only penetrated about an eighth of 

 an inch, and had then died, the head being directed inwards. 

 The female of this species ordinarily burrows horizontally and 

 the larvae vertically, the contrary being the habit of the scolytus 

 of the elm." 



The accompanying figure i^Jig. 73.) represents part of one of 

 these twigs, m showing the burrow made by the insect at n. It is 



a remarkable circumstance, that this stripping off" of the young 

 twigs takes place annually, without the death of the tree being 

 a necessary consequence ; thus proving that it is the burrowing 

 of the larva which is the cause of the mischief. In the case of 

 the elm, however, the burrowing of the males and females into 

 the inner bark, in order to obtain a supply of the viscid sap, or 

 cambium, and their subsequent exit, leaving the orifices of their 

 burrows open, produces of itself great injury to the tree, not 

 only from the exudation of sap from the numerous wounds, but 

 also from the entrance of rain, which by degrees filtrates into 

 the inner bark, and causes a disorganisation of the vessels for 

 an extent of several inches, which is not only indicated, on raising 

 the bark, by a large black patch moistened by a black fluid, but 



