6998 



Entomological Society. 



some cause or another, it had suddenly, as it were, come to an untimely end ; and 

 such a tree we had in the Gardens ; I watched it in its beauty, and in three years saw 

 it cut down and carried away dead ; but what a sight met our view on removing the 

 bark ! — the surface of the trunk, as many gentlemen will remember (for I exhibited a 

 piece of it, 3 feet long, before this Society), was beautifully scored by the lateral tubes 

 of the Scolytus larvae ; and we reckoned that this solitary tree gave birth to no less 

 than the prodigious number of 280,000 perfect insects! Well may we be transfixed 

 with astonishment; but the greater wonder is that an elm should still be found to 

 grace our ornamental parks. I may now fairly presume to state that the 18 sickly 

 trees were not in the least suffering from defective nourishment at the roots, nor had 

 their stems been embanked in soil ; and yet many of them were evidently dying; but 

 one thing was very apparent, namely, that in proportion to the sickly condition of the 

 tree so we found the increase of Scolyti. And this leads us to the second question, — 

 Does the attack of the Scolytus prove injurious to the tree ? 



" The Scolytus destructor is known to many present ; it is a small dark beetle, be- 

 longing to the family Bostricidae of Leach. When the first warmth of spring sets in 

 the perfect insect escapes from beneath the bark, by eating its way out; the female 

 soon after selects a tree for the purpose of depositing her ova; she commences her per- 

 foration always beneath a little projecting piece of bark at the upper end of a crack; 

 she bores inwards and upwards until on the surface of the alburnum, when she ascends 

 direct; the tube thus formed is from 2 to inches in length, Jths of a line in diame- 

 ter, and of equal size throughout, except at a short distance from its entrance, where 

 a small cavity is usually found sufficiently large to allow the parent insect to turn ; on 

 each side, in small crenules, she deposits her eggs as she advances, and closes the 

 aperture with some plastic material ; the number of eggs is in proportion to the length 

 of tube (and this is very much influenced by the condition of the under surface of 

 the bark, for if the Scolyti abound the parent ceases boring, so as not to perforate the 

 workings of another when she approaches it) ; only a small septum divides each ; there 

 are generally from 60 to 70. On bursting their shells the young larvae immediately 

 commence feeding on the last deposit of alburnum ; they at first form parallel trans- 

 verse lines or tubes, which are seen to gradually enlarge and diverge, and are filled 

 with exuviae as the larvae progress onwards ; their increasing size now oblige those 

 larvae first hatched to bore downwards, the centre ones outwards, and the last upwards ; 

 here they continue to feed during the summer, autumn and winter (if mild) : when 

 full-grown they form a case, in which they change to the pupa state ; and then, at the 

 end of May or beginning of June, they eat their way out through the substance of the 

 bark, and leave those shot-like holes showing their plan of exit : they now fly about 

 for a short time, and then the females commence the process for perpetuating their 

 species, by laying their eggs. I believe after they have once commenced boring and 

 depositing their ova they never take wing again : as soon as the female has deposited 

 all her eggs, with her head pointing inwards, she dies at the entrance of her tube, 

 thus, as it were, even in death performing a maternal duty, by closing the aperture to 

 her young ones with her dead body. It is very rare to find a parent tube without the 

 insect, although no doubt they occasionally become a prey to various smaller insects. 

 It is the frass the female ejects from the tube that leads to the detection of the pre- 

 sence of the brood, for were it not for this fortunate circumstance we should never be 

 apprised of the destruction going on within the tree until the escape of the mature 

 insect, in spring, shows the exit-holes. 



