grossulariae Kalt., and Aphis viburni Schr. 267 



June and July I worked with alate and apterous individuals of later 

 generations. The results are set out in the accompanying tables 

 from which it will be seen that out of thirteen attempts to transfer 

 A. viburni to Ribes rubrum, in only two cases did the resulting 

 colonies survive more than ten days, while reproduction was very 

 feeble and never occurred beyond the third generation. In one 

 case (Table A, Number IX) an attempt was made to re-transfer the 

 third generation back from the currant to the guelder rose, but 

 the result was that the aphides all died within twenty-four hours. 



Similar attempts were made to transfer A. grossulariae from 

 currant to guelder rose, but the colonies never survived more than 

 six days, and reproduction was very feeble. Meanwhile the natural 

 colonies on guelder rose and currant flourished from the end of 

 May to the middle of August and end of July respectively. 



Aphis grossulariae has not been recorded from other food plants, 

 but during June I observed three instances where winged migrants 

 had established themselves on the flower heads of the Canterbury 

 Bell {Campanula) and the resulting colonies persisted for two or 

 three weeks. 



The conclusions suggested by the foregoing observations are 

 that, as Theobald points out, A. grossulariae is probably identical 

 with A. viburni. The first migrant from the birth plant ( Viburntmi) 

 can form colonies either on Viburmim, which is the natural host, 

 or else on Ribes. The descendants of the migrants to Viburnum 

 may with some difficulty be established on currant although the 

 resulting colonies are not so strong as those derived from an early 

 migrant. On the other hand the descendants of the migrants to 

 currant cannot be re-established on Viburnum. It seems as if in 

 two or three generations some change takes place in the currant 

 form which prevents it from flourishing on the guelder rose. One 

 explanation is that there is some change in the constitution of the 

 guelder rose plant — an increase of tannins for instance — and that 

 the strain on guelder rose can gradually adapt itself to altered 

 conditions which the newly transferred currant reared stock cannot 

 tolerate. But this explanation is not wholly satisfactory because 

 the dates show that unsuccessful transferences took place in the 

 second and third generations while the plants were still young, 

 while the most successful attempt was made in July when the 

 shoots were mature. It is also worth noticing that while the more 

 successful attempts were made with winged parents, yet in several 

 of the Viburnum-io-cnvYajxt experiments, wingless females were 

 found to feed and reproduce on the new host. 



Theobald {op. cit. p. 100) suggests that A. grossulariae maybe 

 the alternating form of A. viburni, but says that he has twice 

 failed to transfer the former to Vibui^num — a result confirming my 

 own experiments in Table B. On the other hand, it is possible that 



