311 



ON THE SEXUAL FORMS OF APHIS SALICETI, 

 KALTENBACH. 



By maud D. HAVILAND, 



Fellow of Newnham College, Cambridge. 



In June 1919, while collecting numbers of Aphis saliceti, Kalt., from the 

 sallow tree {Salix caprea) for the study of their hymenopterous parasites, 

 it was found that the material chiefly consisted of sexual males and 

 females, not of parthenogenetic individuals as might have been expected 

 at that season. It is known that this aphis differs from most Aphidinae 

 in the appearance of the sexuales at mid-summer instead of in the autumn, 

 and their occurrence at this season has been observed both on the Conti- 

 nent and in America^. But hitherto they do not seem to have been 

 recorded in this country, and as, so far as I know, there is no detailed 

 description of these forms, one is appended. 



There is some discrepancy in the earlier accounts of this species. 

 Von Baehr {Archiv. Zellforsh., 1919), who found the sexuales in Germany 

 in May, says that Kaltenbach and de Geer also observed their appearance 

 in summer ; but reference to Kaltenbach [Monograpliie der Pflanzenlausen, 

 Aphiden, p. 131) shows that this observer did not find them himself, 

 though he records that de Geer found summer sexuales of Aphis solids, 

 which from the description is certainly a synonym for Melanoxanthus 

 solids, Buckt. Von Baehr supposes that this is a confusion (Verwech- 

 selung) between the two species, but from de Geer's description {Memoires, 

 III., 11, 76) it is possible that the latter was in fact speaking of Melono- 

 xanthus. He remarks on the row of white spots on the body, "puceron du 

 saule aux taches cotonneuses," and describes the type as " obscure viridis, 

 tuberculis lanuginosis albis, corniculis longioribus." The long cornicles 

 apply better to Aphis saliceti than to Melanoxanthus solids, but the 

 pilose white patches cannot possibly refer to the* former species; and 

 Kaltenbach, who was acquainted with both forms, accepts de Geer's 

 solids as synonymous with his own. De Geer describes the male as dark 

 yellow. Thus the possibility suggests itself that Melanoxanthus, which, 



1 1906. Stevens, N. M. Carnegie Institute, Wash., pvb. 51. 

 1918. Gillette, C. P. and Bragg, L. C. Can. Ent, Vol. L., no. 3. 



