150 TRANSACTIONS OF ROYAL SCOTl'lSH ARBORICULTURAL SOCIETY. 



{b) Larch. 



Larch has been widely planted in this country under 

 conditions very different from those of its natural habitat, with 

 a consequent weakening of the tree. This has made this conifer 

 specially sensitive to its enemies in general and to Chermesidae 

 in particular. In most cases the species of both the genera 

 Chermes, s. str., and Cnaphalodes are present on the same tree. 

 The former is principally a bark feeder while the latter is a twig 

 and leaf feeder, hence the one genus supplements the other to the 

 detriment of the host. 



(i.) Genus Cherjnes, s. str. — The Colonici are frequently so 

 numerous as to whiten the bark of the trunk and branches of 

 larch. After such an attack the bark usually turns black. As 

 a rule the Colonici avoid strongly lighted parts of the tree, such 

 as tops of exposed trees and upper sides of branches. The 

 feeding of the numerous Colonici, at a time when growth 

 should be at a maximum, must have a weakening effect on the 

 tree. The punctures are a possible source of infection by 

 wound parasitic fungi. The Sexuparge generally feed on the 

 needles of the elongating shoots, but as the duration of the 

 feeding is short the damage is unimportant. 



(ii.) Genus Cnaphalodes. — The Colonici feed on the dwarf 

 shoots of older trees and on the bark of the branches and trunk 

 of young trees of larch. The Colonici are frequently very 

 numerous. The species of this genus are generally the first to 

 attack the larch trees and are the species generally found on 

 larch nursery stock. The species of Chermes, s. str., attack 

 later on. In my opinion, the species of Cnaphalodes do the 

 greatest damage in the Progrediens stage. The three or more 

 generations of Progredientes feed on the larch needles during 

 the summer, and are frequently so numerous as to whiten the 

 needles of this conifer. As a result of this attack, the dwarf 

 shoots and dormant buds may begin to grow. These succulent 

 shoots, together with the elongating terminal shoots, provide 

 additional food for the succeeding generations of Progredientes, 

 so that the struggles of the tree to free itself only result in its 

 still further weakening. 



In my opinion the collective damage done to larch by the 

 species of the two genera Chermes, s. str., and Cnaphalodes, is 

 serious on many areas in this country. 



