48 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



from the elm rosette continue to settle upon apple and their progeny 

 continue to have the characters of S. lanigera — at least in Maine. It 

 is going to be interesting, by the way, to see how this species squares 

 itself Avith that type of life cycle in certain localities. In Europe, for 

 instance, even where the "woolly aphid of the apple" is troublesome, 

 we have no published record of the rosette aphid of the elm. How 

 does it get along there? Sustains itself by continuous parthenogenetic 

 generations? At any rate it lias not lost its habit of fall migrations 

 according to the reports of Borner^ and Ileh.^ Is it possible that it 

 exists on the European elm but less conspicuously than on the Ameri- 

 can? 



But why should it not be a simple matter — the mere finding out 

 whether a species is migratory? Partly because every aphid cycle we 

 learn is as likely to mislead as to guide us with the next species we 

 investigate. We are in the habit of saying, for instance, that we know 

 that Aphis pomi, Myzus cerasi, and Schizoneura rileyi do not migrate 

 because they occur at all times of the year upon a single food plant, 

 respectively the apple, the cherry, and the elm. That in itself is no 

 reason for surety, for Prociphilus tessellata, P. venafuscus, and Schizo- 

 neura lanigera each ocows at all times of the year upon a single food 

 plant, respectively the alder, the balsam fir, and the apple, and yet 

 these are all migratory aphids. There is this distinction between 

 these two cases, however, the three species first mentioned occur at 

 all times of the year upon their primary food plant and the second 

 three do not — with them it is their secondary food plant which harbors 

 them for twelve months of the year in addition to their winter and 

 spring residence upon their primary host. By "primary host" is 

 understood that plant upon which the over-wintering egg is normally 

 deposited and upon which the stem mother and her immediate progeny 

 develop. The "secondary host" is that plant to which the spring 

 migrants fly and from which they return to the primary host. At 

 present I know of no member of the Subfamily Aphidiruc which resides 

 for twelve months upon its primary host and in addition migrates for 

 a part of the year to a secondary host. But it would be a rash per- 

 son who felt safe in the conviction that such a cycle could not be. 



Many migratory aphids, to be sure, alternate their primary and 

 secondary host plants at regular intervals, each time entirely desert- 

 ing the one for the other, thus existing for a part of the year only 

 upon each. Rhopalosiphum nympheae Linn is an example of such a 



^ 1909. Die Blutlausplage unci ilire Bekampfung. Kaiserliche Biologische 

 Anstalt fur Land- und Forstwirtschaft. Flugblatt Nr. 33, p. 2. 



2 1913. Neues von der Blutlaus. Der praktische Ratgeber im Obst-und Garten- 

 bau. Nr. 5, p. 44. 



