CHERMESID^ IN RELATION TO BRITISH FORESTRY. 1 43 



there is a normal migration of this species between these two 

 hosts in their natural habitat. 



(1) Fuudatrix Generation. — None in Europe. 



(2) Gallicola Generation. — None in Europe. 



(3) Colonici Generation. — The cycle is similar to that of 

 Pineus pini, but only on Weymouth pine {Pinus strol)us). No 

 Colonici alatce have been observed in Europe. 



(4) Sexupara Generation. — In Europe the Sexuparae migrate 

 to common spruce {Picea exce/sa) and perish. 



(5) Sexuales. — None in Europe. 



3. Spruce-Silver Fir Series. 



This series is made up of one genus in this country, the genus 

 Dreyfusia (Borner). There are two species of this genus, 

 namely, Dreyfusia picece (Ratz.), Borner, and Dreyfusia Niiss/ini, 

 Borner. The former lives entirely on various species of silver 

 fir, while the life-cycle of the latter is passed on Picea orientalis 

 (rarely on P. exce/sa), and on Abies nordmanniana and A.pecfi?idta. 

 The history of the silver fir Chermes is very interesting. It 

 appears that only the species named by Ratzeburg as Chermes 

 picecz was originally present in Europe. This species is typically 

 found on the bark of old silver firs and does little damage. 

 Later the silver fir Chermes became a much more serious enemy. 

 Abies nordmanniana was first of all principally attacked, but 

 later A. pectinata, the indigenous silver fir, also fell a victim. 

 For a long time it was not known that a new species had made 

 its appearance. Cholodkovsky, Niisslin, and others, however, 

 observed that while the old Chermes picece. lived entirely on silver 

 fir, the winged forms now arising on that conifer migrated to 

 Picea exce/sa, but only very rarely completed its cycle on this 

 spruce. Cholodkovsky considered this migrating race to be the 

 species which Dreyfus had observed and named as Chermes 

 funitectus. Later it was found that this species completed its 

 cycle on the Oriental spruce, Picea orienta/is. Borner pointed 

 out the structural differences between the two species. He 

 rejected the specific name '■'' funitectus, ^^ as Dreyfus had originally 

 found that species on Tsuga canadensis; but probably Dreyfus 

 wrongly identified the host. Borner named this species Dreyfusia 

 Nilss/ini. Marchal has closely studied the life-histories of the 

 two silver-fir species, and his conclusions have, in the main, 



