APHIDIDyE. 285 



oblique vein. The antennte are normally Hve-jointed. The rostrum 

 is very short, being used exclusively as a feeding-organ, and not 

 specially for anchorage. The creature develops three or more long 

 hairs, or setse as they are termed, by means of which it maintains 

 a hold on the bark. In this respect it very much resembles the 

 Diaspinse, or scale-insects, on the ash, alder, willow, &c., as in both 

 families the creatures may be seen dangling in the air, after they 

 have been detached from the bark by birds or other natural enemies. 

 There are no cornicles. The parthenogenetic females secrete wax, 

 and for the most part show, on careful examination, clearly marked 

 chitinous plates. 



Sun(>p><i^ of the Species. 



Producing comparatively large galls on the terminal and lateral 

 shoots of the spruce (Picea e.rrelsa). The shoot often extends 

 beyond the gall ..... C. viridis. 



Producing comparatively small, hard, close galls on the terminal 

 buds of twigs of spruce, and always arresting subsequent 

 growth . . . . . . . G. dwhilohius. 



Producing a white covering on the .stems or foliage of compara- 

 tively young larch-trees . . . . C. lands. 



Producing a white covering on the twigs or branches of young 

 Scots pine or Austrian pine . . . . C. pini. 



Producing a white covering on the branches or stems of Wey- 

 mouth pine ...... C. cortiralis. 



Producing a white covering on the stems or foliage of silver fir 

 (Abies pectinata) or Abies Nordmanniana . C. picece. 



Chermbs viridi« (Eatz). 



This is a gall-forming species on the common spruce {Picea exceha), 

 the gall being in appearance like a pine-apple or pseudo-cone of Scots 

 pine (fig. 269), each abortive shoot terminating in abortive leaves. 



The structure of the gall varies, as in some cases it surrounds the 

 young shoots, and arrests or retards future growth. At other times 

 it may be found on one side of the shoot, thus doing only partial 

 damage. When the leading shoot is attacked, the young tree is often 

 very much injured. This variation of gall-formation is sometimes put 

 down as the work of different species of Chermes. 



