APHIDID^E. 



333 



to fully clear up the life -history of this hitherto partially studied 

 genus. The aspiring student should therefore collect the various 

 species of what hitherto has been termed stem-mothers on different 

 trees, boil them in caustic potash, and stain with Oawshaw's magenta 

 penny dye, as recommended for scale-insects, and try to verify the 

 various minute points of structural difference as shown in fig. 309 

 from Judeich and Mtsche, carefully noting and tabulating the results 

 of his observations. Such a method would obviously be highly 

 interesting and important, as in searching for the various anticipated 

 alternating stages of the same insect on different trees, confirmation 

 of the same creature changing from host- 

 plant to host- plant would obviously be 

 ratified. 



Importance of the Genus Chermes 

 ix Forestry. 



This genus is exclusively arboreal, and 

 should be specially studied from a practical 

 and scientific point of view. To the 

 scientist the various species of insects 

 chance from one tree to another, and thus 

 our so-called species are simply various 

 stages of the same insect. But the prac- 

 tical man, often indifferent to specific dis- 

 tinctions, recognises the injurious effects 

 on certain trees, and thus prefers to 

 identify the species as coincident with 

 the food - plant. Thus Chermes laricis 

 may often be found very injurious to young larches of from ten to 

 fifteen years of age, more especially on those trees growing in hollows 

 or in damp spots; Chermes abietis on spruce-trees Avhich are not 

 growing in suitable places, and often in young spruce -trees in the 

 nursery-lines ; and Chermes picece is often found on young silver firs 

 in the nursery, and on young trees of A. Nordmanniana. C. strobi- 

 lobius is perhaps more destructive to young trees in the wood, especially 

 those too much overshaded and not thriving well. The dead galls 

 adhere very closely to the twigs, and can often be seen after the 

 infested tree is partially dead. 



Fig. 308. Chermes picese on 



bark of silver fir. 



