12 Mr Burdon, The Pine-apple Gall of tlie Spruce: 



The Pine-apple Gall of the Spruce: a Note on the early stages 

 of its development*. By E. R. Burdon, B.A., Sidney Sussex 

 College. 



[Bead 31 October 1904.] 



The galls are caused by the hibernating generation of certain 

 Aphidae belonging to the genus Chermes, which lives exclusively 

 on coniferous trees. 



Several species of Chermes have been described by continental 

 writers, two of which (G. abietis and C. strobilobius) are certainly 

 present in Britain, and further search will probably result in 

 others being found. 



The insects have a most complicated life-cycle which has been 

 worked out by Dreyfus, Blochmann and others in Germany, and 

 Cholodkovsky in Russia. This cycle exhibits a hetercecism similar 

 to that which obtains in Flatworms, Uredineae, etc. The main 

 facts are briefly set forth in the following table, in which the 

 successive generations are denoted by biologic names f. 



Of these various generations it is worthy of note that only one 

 of them — the Fundatrices on the Spruce — induces the formation 

 of a gall, though all are equally engaged in sucking either on the 

 stem or needles. 



The galls caused by the different species of Chermes all follow 

 the same general plan of development, and, although there are 

 slight differences in detail, the following account, which refers 

 specially to the galls of C. abietis, probably represents what occurs 

 in every case. 



The life of the gall is naturally divided into three distinct 

 stages : 



(1) its development whilst still enclosed in the bud-scales ; 



(2) its development after emerging from the bud until the 

 opening of the chambers and exit of the inhabitants; 



(3) its death, decay and subsequent fate. 



In the present paper my remarks are limited to the events 

 which occur during the first stage. 



* Figures and full details will appear in a later paper. The present communi- 

 cation merely summarises the most important points and conclusions. 



t For fuller details see Prof. Cholodkovsky's " Beitrage zu einer Monographie 

 der Coniferen-Lause," Horae Soc. Ent. Ross. xxx. pp. 1 — 102, and xxxi. pp. 1 — 61. 



