CHERMES ABIETIS. 361 



and on 4- to 8- year-old shoots of willows. Salix triandra, 

 L., S. fragilis, L., and S. alba, are all attacked. The 

 maggot bores horizontally through the bark, in which 

 from July to the following April it excavates short irregular 

 vertical galleries. This causes the appearance of spindle- 

 shaped swellings of the bark and underlying wood, at least in 

 the larger stems, which eventually become rough owing to the 

 irregular detachment of the bark. Pupation takes place in 

 the same spots, and the emergence of the flies riddles the bark 

 with small holes. 



This species is sometimes decidedly common and injurious 

 to planted willow cuttings. The only satisfactory treatment 

 is the timely cutting-off and burning of the infested shoots 

 before emergence of the gnats. 



The family of Cecidomyiidae also contains the Hessian-fly, 

 C. destructor, Say, one of the greatest of pests to cereal crops, 

 and various species attacking conifers, of which C. kellneri, 

 Hnsche., gives rise to galls on the buds of larch. Others pro- 

 duce galls on beech leaves (C.fagi, Htg.), and on birch leaves 

 C. letidae, Wtg. 



C. Hemiptera, 



FAMILY I. APHIDIDAE (PLANT-LICE). 

 Description of Family. 



Insects with long, usually filiform or setose antennae, of 3 to 7 

 joints; ocelli either absent or 3 in number; rostrum usually 

 well developed. Wings membranous, often absent, especially 

 in ? . Legs usually long and thin ; tarsi of 2 joints. They 

 move by flying, or running. 



The species of Chermes comprise those aphides, that are of 

 most importance as being injurious to forest-trees, especially 

 to coniferae. 



The mode of life of plant-lice is as follows : The hard- 

 shelled eggs that resist the cold are laid during autumn in 

 rows or groups on needles, leaves, buds or shoots, and hiber- 

 nate. In the spring, small wingless $ producing parthenogenetic 

 wingless ? issue from the eggs, and thus several generations 



