INDIRECT INJURIES CAUSED BY INSECTS, 181 



Paris, that 40,000 trees were killed by it ; and many of the 

 finest elms in St. James's Park and Kensington Gardens \ as 

 well as in the promenades of various cities in the north of 

 France, have fallen victims to another of this tribe, Scolytus 

 destructor J, whose trivial name well characterises the frequency 

 and severity of its ravages. ^ 



1 MacLeay in Edin. Phil. Journ. xi. 123. 



2 While residing at Brussels in the spring of 1836, having pointed out to 

 Dr. George, Professor of Botany at the University, that many of the elms in the 

 park were infested with this insect, and that there was eminent risk of this noble 

 promenade, which consists almost wholly of elms, being destroyed by it, he 

 brought the subject under the notice of the burgomaster and municipal council, 

 who very wisely had the diseased trees cut down, as well as the many much 

 younger but equally infested trees of the Boulevards, and the bark of the whole 

 peeled off and carefully burnt. I afterwards found, in a tour along the north 

 coast of France through Normandy, &c., that the elms in the promenades (almost 

 always formed of this tree), in all the large towns, were in a course of rapid de- 

 struction by this same Scolytus destructor, particularly at Calais, Boulogne, Rouen, 

 Havre, and Caen ; and numerous observations convinced me that the general 

 opinion that these insects attack only those trees which are previously diseased 

 from natural decay is altogether erroneous, and that Professor Audouin's dis- 

 covery is as important and correct as novel — namely, that though it is quite 

 true that the female Scolyti never lay their eggs except in trees M'hich are in a 

 declining state; yet it is equally certain that the healthiest elms, where Scolyti 

 abound, are constantly brought into this languishing state by the attacks of the 

 males, or, as M. Audouin conceives, of both sexes (see remarks on this point 

 by W. Spence in Trans. Ent. Soc. Lond. ii. proc, xlv. ), upon the hark for food; 

 so that in consequence of the loss of sap from the numerous holes which they 

 gnaw, and the subsequent mischief from the rain penetrating into them, the trees 

 are soon brought into that unhealthy condition which the instinct of the female 

 requires to induce her to lay her eggs in them. (Spence in Trans. Ent. Soc. 

 Lond. ii. ^roc. xiii. xv. xx. xxv. ; Audouin in Ann. Ent. Soc. de France, Bulk 

 Jan. 4. 1837 ; Silbermann, Rev. Entom. iv. 115., where Dr. Ratzeburg is quoted 

 as stating that the large weevil (Pissodes notatus)jn like manner attacks the bark 

 of young pines with its trunk, and thus renders the trees unhealthy before the 

 female deposits her eggs in them.) For a further description of the mischief 

 done by Scolytus destructor, and the means of preventing its extension, see a 

 communication by W. S. under the article Ulmus, in Mr. Loudon's Arboretum et 

 Fruticetum Britannicum ; to which admirable work the reader is also referred for 

 more complete details than could be here given in the valuable contributions by 

 Mr. Westwood relative to insects injurious to this and other species of forest-trees. 



It may be here inentioned, though somewhat out of place, for the purpose of 

 drawing the attention of Entomologists to a new tribe of insect-parasites of 

 which no account appears to have been given in books, that in examining closely 

 the pupae of Scolytus destructor at Brussels, I found them lined in different parts 

 of their external surface, but especially on the throat and about the cases of the 

 elytra, with numerous transparent eel-shaped vermicles, not easily visible to the 

 naked eye from their small size, being not more than one eighth or one tenth of 

 a line in length, but perceptible through a pocket lens, especially when exposure 

 to the air or the warm breath had made them elevate their tails (or heads, which- 

 ever they may be), a movement which sometimes takes place speedily, but at 

 others only after a considerable examination, when they present the appearance 

 of so many animated hairs twisting and curling themselves in various directions. 

 These vermicles, under M. Wesmael's powerful compound microscope, with which 

 he was so good as to assist me in examining them, exhibit not the slightest trace 

 either of mouth or other external organ, nor of intestines, nor of internal vessels 



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