155 



though they have received but little attention in Britain. The nomen- 

 clature of the generations is discussed in detail. A history of previous 

 research on the species of Chermes is given and the technique employed 

 by the various workers on this group in conducting their experiments is 

 described. Recent experiments in Britain were carried out in a small 

 wood at Drumshoreland, West Lothian, which contained Picea excelsa, 

 P. alba, P. nigra, Larix euro])aea, L. leptolepis, Pinus sylvestris, Pseu- 

 dotsuga douglasi and hardwoods. The age of the trees varied from 5 

 to 50 years. 



Chermes (s. str.) was found on the following hosts in Scotland : — 

 Primary or Picea host : Picea excelsa, P. alba, P. orientalis, P. morinda, 

 P. sitkensis. Intermediate or non-Picea host : Larix europaeay 

 L. leptolepis, L. occidentalis. 



Two separate cycles have been proved to be present in Britain : 

 (1). A cycle of two generations, fundatrix and gallicola non-migrans ; 

 these both lay yellow eggs on spruce, and the galls open over an 

 extended period from the end of July until mid-September. This 

 is the species Chermes abietis, Kalt., of Cholodkovsky. (2). A cycle 

 of five generations, fundatrix, gallicola migrans, colonici, sexupara, 

 and sexuales. The fundatrix lays green eggs on spruce, and the 

 gallicola migrans lays very dark green eggs on larch. The galls 

 open during a limited period in the first half of August. This is the 

 species Chermes viridis, Ratz., of Cholodkovsky. There is probably 

 a cycle with both galhcola migrans and non-migrans corresponding 

 to Chermes abietis, L., of Borner, or Chermes occidentalis, Choi. 

 Sistens and progrediens larvae hatch from the eggs laid by the 

 colonici. Many of the sistens larvae do not settle down on the bark, 

 but migrate to the needles and die. 



The genus Cnajjhahdes was found on the following hosts in Scotland : 

 Primary or Picea host : Picea excelsa, P. orientalis, P. alba, P. sitkensis. 

 Intermediate or non-Picea host : Larix europaea, L. leptolepis, 

 L. occidentalis. 



Two separate cycles have been showTi to be present in Britain : 

 (1) A cycle of two generations, fundatrix and gallicola non-migrans. 

 The latter lays bright orange-coloured eggs under the protection of 

 a copious woolly covering. The galls open over an extended period 

 from the end of July until the end of September. This is the species, 

 Chermes lapponicus, Choi., var. tardus, Dreyfus, of Cholodkovsky. 

 (2). A cycle of five generations, fundatrix, galhcola migrans, colonici, 

 sexupara and sexuales. The gallicola migrans lays dark bronze- 

 coloured eggs without any woolly covering on larch. The galls open 

 during a limited period in the first half of July. This is the species, 

 Chermes strobilobiiis, Kalt., of Cholodkovsky. Sistens and progrediens 

 larvae hatch from the eggs laid by the colonici and progredientes of 

 Cnaphalodes strobilobius, Kalt. The relative proportion of each type 

 is variable. It has thus been shown that the above cycles are not 

 confined to North and East Europe, where larch is either absent or 

 the European species is replaced by Larix sibirica, but are present in 

 Britain, where larch and spruce grow side by side. 



On his experimental area the author estimates that 90 per cent, of 

 the species of Chermes and Cnaphalodes on spruce were the non- 

 migrating, parthenogenetic species, although the branches of the spruce 

 and the larch were often interlocked. This fact suggests that the 



(C458) b2 



