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The Genu s Cher mes. 



443 



1 . Chermes is an enemy of trees, but confines its attacks 

 to Coniferas. 



2. The normal and complete life history of a species may 

 take two years. There is a change of host, two different 

 species of Conifer being made use of, one the primary host, 

 and the other the secondary, or intermediate, host. 



3. The primary host is typically the Spruce (Picea sp.); 

 the intermediate host is a Larix, Pinus, or Abies. 



4. The foundresses on the primary host give rise to galls; 

 no galls are formed by the other generations. 



5. In the two years' cycle with change of host there are 

 five different generations : — 



(a) The foundresses : wingless females. 



(b) The migrant daughters : winged females. (Some of 

 these may remain on the Spruce without flying to the in- 

 termediate host, and complete the cycle in one year). 



(c) The emigrants, or colonists — as Burdon happily calls 

 them. These are wingless females. 



(d) A generation which may be in two parallel series : 

 (1) the exiles — viz., wingless females that remain on the 

 intermediate host; and (2) the sexuparce — viz., winged 

 females which fly to the primary host. 



(e) A sexual generation of wingless males and females. 



6. Of these various generations the colonists almost com- 

 pletely resemble their grandmothers in structure and also in 

 habit, save that they do not give rise to galls. The sexuparce 

 resemble their grandmothers both in structure and in habit. 

 The exiles (except that they do not give rise to galls) resemble 

 their mothers and their great-grandmothers in structure and 

 habit. 



7. There are three chief forms in the cycle : (a) wingless 

 virgin females; (b) winged virgin females; (c) males and 

 females. 



8. In certain species the life cycle is completed in one year; 

 the host is a Spruce (Picea), and there is no intermediate 

 host. A wingless generation alternates with a winged, and 

 only females are known. 



9. Exceptionally a species, Chermes viridanus Choi., is 

 found on Larch and Larch only. 



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