60 Mr. F. Walker's Notes on Aphides. 



XVIII. Notes on Aphides. By F. Walker, Esq. In a 

 Letter addressed to W. Spence, Esq. 



[Read 6th September, 1847.] 



Grove Cottage, Southgale, 

 August 16tli, 1847. 



My DEAR Sir, 

 I HAVE received your obliging letter, and I shall be happy to send 

 you any information I can respecting Aphides, but my knowledge 

 of them is as yet very slight. I believe that the dock is one of 

 the plants from which the black bean Aphis (^A. Rumicis), is 

 hatched from the egg in the spring, and that the second genera- 

 tion, which is winged, migrates thence to the bean, pea, thistle, 

 chenopodium, &c. &c. It afterwards settles on a great variety of 

 other plants, but does not appear to thrive on them ; however, it 

 sometimes swarms in great profusion on the laburnum, broom, 

 and furze ; it was very abundant last autumn on the furze near 

 Lancaster, and was accompanied by the male in November, and 

 the wingless female then deposited her eggs on the spikes of that 

 plant. Many, especially the migratory species, have wingless and 

 winged broods alternately, and the migrations of the latter serve 

 several purposes ; they pi'event the extinction of a race which 

 would otherwise follow the withering of its food ; they cause the 

 injury inflicted to be in general but temporary, and they distribute 

 and thereby equalize it over a district or country. I believe that 

 the migrations are merely in search of fresh food for themselves 

 and young ones, and not to deposit eggs, and that, generally 

 speaking, the migratory swarms are all females, the males not 

 appearing till late in the autumn. I began to attend to Aphides 

 last year, and I did not observe any males till October and No- 

 vember, when I saw them in the following species, A. Platanoidis, 

 Betulf^, Fagi, Tilics, Ruhi, Vihurm, Persicce, Rihis, Mali, Sorbi, 

 Dichoda, and a few more. The winged males of the above named 

 species all paired with wingless females previous to the egg-laying 

 of the latter. Some species are always wingless, or perhaps in 

 fine warm seasons a winged individual may now and then appear 

 amongst the swarms ; in other species all the broods are winged 

 till the last, wherein the wingless oviparous female pairs with 

 the winged male; but in the majority of species the wingless 

 and winged generations are alternate, and the second brood are 

 always winged. The best treatises on Aphides that I have 



