February, '16] PATCH: APHID ECOLOGY 45 



It remained for Lichtenstein to announce in various publications 

 during the year 1877 his behef that European species inhabiting elm 

 and poplar migrated to the roots of grasses. 



Rile}' (1879 took him vigorously to task for what he called Lichten- 

 stein's ""theory" explaining patiently that 



Species of the same genus often so closely resemble each other that they are more 

 readily distmguished by their mode of life, or by the galls they produce, than by 

 structural or describable differences; and this holds particularly true of the immatm-e 

 or apterous stages. This fact, taken in connection with what is here recorded and 

 what is already known of the habits of the sub-family, renders it extremely improbable 

 that any of the species subsist at one time on one plant and habitually change, by 

 migration, to another of a totally different nature. 



However, two years later we find Riley writing (1881)-: 



M. Lichtenstein has for some years fully beheved that most of our Aphids, and 

 especially the gall-making Pemphigini, habitually migrate, in the winged, parthe- 

 nogenic, female form, from one plant to another, and that the species must necessarily 

 inhabit two different plants before it passes through its full cycle of development. 

 That it is the rule for most of the insects of this family to so migrate is evident from 

 the fact, patent to all who have observed them, that there is a period in mid-summer 

 when most of the species abandon the plants which they so seriously affect in spring 

 and early summer. . . . The fact of migration rests, moreover, on repeated dii-ect 

 observations, and all spring gall-inhabiting species have usually vacated their galls 

 by mid-summer. ... In fact it is now coming to be well understood, that in this 

 family the habit of the same species in spring is quite different to its habit in the 

 fall, and that in the study of the insects of this family there is opened up to us a 

 new and interesting field for observation. . . . We have for some time since 

 recognized this fact of migration, but have been led to believe from the known facts 

 in the case that the migration was necessarily from one plant to another of the same 

 genus. M. Lichtenstein, on the contrary, believes that the change is still more 

 wonderful and that many tree-inhabiting and gall-mal\ing species actually have a 

 mid-summer life on the roots of grasses and herbaceous plants. He has recently 

 communicated to us some discoveries that certainly justify his views. 



The pioneer work in America in this "new and interesting field 

 for observation" appeared in 1889^ with the announcement of the 

 identity of Schizoneura panicola Thomas and S. corni Fab., followed 

 in 1890'* by a fuller account with details of observations and experimen- 

 tal data showing that S. -panicola is merely the grass-root form of 

 the ancient Cornus aphid. In this synonomy was included *S. vemista 



U879. Bulletin U. S. Geological Survey. Vol. V, No. 1. Biological Notes on 

 the Pemphigina?, with descriptions of new species. 



^881. The American Naturalist, Vol. XV, pp. 819-820. Migrations of plant- 

 lice from one plant to another. 



3 1889. Insect Life, Vol. II, pp. 108-9. 



^ 1890. U. S. Dept. of Agri., Div. of Ent., Bui. No. 22, pp. 32-41. The grass- 

 root plant-louse alias the dogwood plant-louse. 



