174 INSECTS INJURIOUS TO FOREST TREES. 



S - i hey comniit upon the young growth of the trees they fasten 

 upon is always hurtful, and often the cause of irremediable injury. 

 It has been calculated by Professor Owen of London, in one of 

 his lectures on M Comparative Anatomy/' that a single aphis {Aphis 

 larUffera) is capable of producing the enormous multitude of 

 1,000,00''. >,000— one quintillion— in a year, which 



affords some explanation of the vast multitudes in which these 

 insects often appear. They live upon the young and tender 

 wood and leaves, sucking the sap, and causing the leaves to curl 

 up or blister, ultimately turning yellow, and dropping off prema- 

 turely, to the great and often permanent injury of the tree. The 

 aphis emits the well-known honey-dew, so common on trees and 

 hedges in spring and early summer, which is very deleterious to 

 vegetation, by clogging up the stomata of the leaves upon which it 

 is deposited, attracting other insects, and collecting dirt upon the 

 surfaces of the leaves, which is not beneficial to them. From the 

 investigations of some of our most eminent entomologists, it 

 appears that almost every species of plant has a variety of aphis 

 peculiar to it, and upon which alone it feeds ; but it may suffice to 

 mention one of the most mischievous to forest trees, viz., the larch 

 aphis {Addgis lands), which has been so fully treated in the 

 Transactions of the Society, by Mr M : C'orquodale, forester", Scone 

 Palace, Perthshire (see vol. ii, p. 45), and the able and interest- 

 ing paper, read by Mr Gome of Piait Lodge, Trinity, Edinburgh, 

 at our meeting last year, and printed in the Transactions, vol. 

 viii, p. 61, in which papers are given full details of the grievous 

 injury inflicted upon the larch by the aphis. Another variety of 

 aphis well known to foresters. Aphis cro.t<ngi, or the thorn-fly, in 

 some seasons does a vast amount of injury to young thorns in 

 nurseries and hedgerows. 



The chief means of destroying the aphides is tobacco, in some 

 shape or other. So far as I am aware, there is no practicable 

 way of destroying the aphis when it attacks large trees, except 

 the fina l one, cutting down and burning. 



To get rid of them on young trees in nurseries or plantations, 

 when it is thought worth the trouble, the best remedy is diluted 

 tobacco juice, applied by a syringe or engine to every part of 

 the plants on which an insect can be seen. There are many 

 other methods for eradicating the aphis from trees recommended by 

 various authorities, some being applied in the same way as the 

 tobacco liquor, such as a decoction of bitter aloes, laurel leaves, 



