252 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



with the Chermesidae, its members, like the chermes, having two 

 hosts and a cycle of five alternating generations. Nusslin has 

 described the life-history of the "silver fir root louse "which 

 alternates between ash {Fraxinus) and silver fir, and Tullgren 

 has described one which apparently alternates between honey- 

 suckle {Lonicera) and spruce. Hartig has described a root 

 aphis on spruce which he named Rhizo^narea piceae, and 

 Tullgren has no doubt that this is the apterous parthenogenetic 

 form of a Pemphigid and renames it Pemphigus piceae. A 

 comparison of Tullgren's description of this species and of the 

 aphis found on pine-roots in Britain indicates that this P. piceae 

 is probably the species concerned. Efforts were made to trace 

 the life-history of the pine-root aphis at Kew, but owing to an 

 accident to the plants used for rearing experiments no result 

 has been obtained so far. The question as to the identity 

 and life-history of this insect is both interesting and important, 

 and any information as to the occurrence of this aphis, and 

 as to any injuries it may cause, would be welcomed. 



J. W. M. 



A Parasite of the Poplar Saw-Fly. 



During the summer of 192 1, whilst rearing two species 

 of saw-fly {Croesus septentrionalis, Leach, and Trichiocampus 

 viminalis. Fall) in the Entomological Laboratory, Royal 

 Botanic Gardens, Kew, it was found that out of a dozen 

 larvae of T. viminalis which spun up in the corners of 

 the breeding cages, only some, three or four yielded saw-fly 

 cocoons. From the remainder, Tachinid flies were obtained 

 between 19th August and ist September: these were identified 

 by Major Austen of the British Museum as Ptychomyia selecta, 

 Meigen. A brief note on T. viminalis appears in The Scottish 

 Naturalist, September-October, 1922, but it may be of interest 

 to give here some account of the parasite obtained during the 

 rearing experiments. 



Baer {Die Tachinen, Berlin, 1921) states that Ptychomyia 

 selecta is a parasite of the long-horned Hyponomeutid moths, 

 and a frequent enemy of several saw-flies, including T. viminalis 

 and a species of Lophyrus. P. selecta is a small fly not unlike 

 the lesser house fly in general appearance. It belongs to 



