The Elm and its Insect Enemies. 191 



THE ELM AND ITS INSECT ENEMIES. 



BY SHIRLEY HIBBERD. 



In a paper entitled " Insects Injurious to the Elm/' by Mr. H. 

 Noel Humphreys, which has appeared in this work (August 

 1862, p. 28), mention is made in somewhat approving terms of 

 M. Robert's proposal to disbark elm-trees, in order to recover 

 them from the diseases alleged to be caused by the attacks of 

 insects. Observations extending over many years, varied occa- 

 sionally by direct experiments, have convinced me that the elm 

 enjoys an almost total immunity from the attacks of insects, and 

 that, therefore, the accusations made against Scolytus destruc- 

 tor and Cossonus linearis are entirely unfounded, or rather have 

 their foundation in a misconception of the facts. When so able 

 a writer as Mr. Humphreys espouses Robertism, there is danger 

 to be apprehended, and to avert that danger, I assert, in the 

 first place, that neither Scolytus nor Oossus ever injure healthy 

 trees, and that if they did so, the system of M. Robert would 

 be more likely to hasten their death than their recovery. Mr. 

 Humphreys has so truthfully and explicitly described the in- 

 sects themselves, and their modes of boring and tunnelling in 

 the tree, that there will be no occasion to refer to that part of 

 the subject, except to point out the sources of error in the 

 application of the facts. 



It may be as well to state that there is nothing new in the 

 hypothesis which assigns the death of elm-trees to the ravages 

 of xylophagous insects. 



There has been much written on this subject, and in nearly 

 every case the writers have adopted arguments similar to those 

 used by Mr. Humphreys, who, so far, is perfectly orthodox in 

 concluding that as these insects are found in diseased elms, 

 that therefore they are the cause of the disease. In the Edin- 

 burgh Philosophical Journal, 1824, is an account by Mr. 

 M'Leay of the decay of elms in St. James's Park, in which he 

 attributes their destruction to Scolytus. In Curtis' 's Illustra- 

 tions of British Entomology , No. 11, is an admirable figure of 

 Scolytus destructor, with a description in which the allegation 

 of its destruction of elm-trees is repeated. In 1827 there was 

 published in the Cambridge Chronicle (November 9), an account 

 by Mr. Deck, of the decay of some elms in the front of Catha- 

 rina Hall, in which he said — ' ' their death has been decidedly 

 occasioned by the ravages of a small beetle of the genus Scoly- 

 tus, and of the species emphatically termed ' destructor.' " 

 An admirably written reply to this, by Mr. J. Denson of 

 Waterbeach, appeared in the Magazine of Natural History, 1830. 



