Insects. 



6147 



from you, which I was very glad to see, in reference to the article by Captain Cox on 

 Scolytus destructor and Cossus ligniperda. Now, as regards the latter feeding in 

 elms, I had an instance of this lately brought before me: the Rev. J. Hiilens was 

 pupa digging this spring, and came lo an elm that was greatly damaged by the boring 

 of a whole brood of larvae of the Cossus, eighteen in number, or rather this is the 

 number that gentleman brought home with him, some of which he gave to me : thus 

 it will be seen that Captain Cox is right so far as the Cossus will feed in elm timber; 

 but, as you observe Zeuzera ^sculi might have been mistaken for it if the larvie were 

 not seen, and as the larvae of the latter are so common in the parks and even in the 

 squares of London, it is very probable to have been that species. Now, as regards the 

 Scolytus destructor, I disagree with Captain Cox in saying the insect attacks healthy 

 trees ; for my part T do not believe it does so. In the neighbourhood of Exeter and in 

 Devonshire generally, the elm is the most common tree we have, indeed it is the 

 principal arborescent vegetation of the couuly ; and you may hunt a hundred, nay a 

 thousand, healthy trees and you will not find a single instance of the Scol) tus; but if 

 a tree is diseased so as to cause a stagnation in the sap in any part of the trunk or 

 large limbs, but more particularly the former, it is near to this you will find the larvae 

 of the Scolytus in plenty feeding on the liber and cambium, as also the softer portions 

 of the wood immediately beneath : it is on the mucilaginous sweet sap that the larvae 

 appear to subsist; and where disease has taken place either from a wound, or the decay 

 of a branch so as to admit water and the weather to act directly on the young and 

 delicate wood forming liber, the cells become ruptured and broken down ; the conse- 

 quence is, the portions of the inner bark become so gorged with sap, that it oozes out 

 and becomes a weeping wound ; and it is round about such wounds you find the larvae 

 of this insect feeding on this gorged portion of the liber, which is very sweet to the 

 taste : like most other insects they appear to like saccharine fluids. Now, to prove 

 that the insects prefer the stagnant sap to that of an healthy tree, I will instance a 

 great number of elms that are cut down for timber and brought into the basin yard, 

 near the quay and the steam saw-mills ; in the bark of several that were cut down in 

 the winter and early spring of 1856— so that they laid in the yard through last 

 summer — and as I was hunting over the trees in this yard for Coleoptera in March 

 and April of this year, and in ripping off* the bark of the elms I discovered it was full 

 of larvae — they literally swarmed with Scolytus larvae; indeed, tliey were so numerous 

 that I was doubtful if it was that species. Well, I left them for some time until I 

 thought they would have arrived at the pupa state, but when I returned to the trees 

 again I found them all stripped of their bark by the poor people from the city, who 

 steal it to burn. I was much vexed to think I could not follow up my observations: 

 I hunted round the trees and found a piece of bark round a small knot, about the size 

 of my hand; when taken off I saw several pupae. I took this piece home and placed 

 it in a breeding-cage, and, about a fortnight ago, five perfect Scolytus emerged from this 

 little bit of bark ; this I. was much pleased to see, as it bore out my supposition. Now 

 I can positively assert that all the trees that I examined in the first instance before 

 the bark was removed were as full of larvae as this sirKill bit I took home with me, 

 and, if they had remained untouched, would have produced thousands of the Scolytus, 

 and these insects would have emerged just in time to deposit their eggs in the bark of 

 the newly brought-in trees which have beeu cut down this last winter and spring; and 

 here I may observe is the place to examine if the limber be sound and good, which I 

 can assure you it is ; so that it is the stagnant sap that attracts the insects, not the 



