ELM LEAF ROSETTE AND WOOLLY APHID OE APPLE. 335 



The other species to which the name Schisoneura americana has been 

 commonly applied is the aphid discussed in Bulletin 241 of this Station. 

 Since the name lanigera takes care of the rosette species on elm as 

 v/ell as on apple, 5". americana seems to be left conveniently for the 

 aphid curling or rolling the leaf of the American Elm (Fig. 45 of Bulle- 

 tin 241). Riley's description of the leaf deformations caused by 

 5". americana^ indicates clearly enough that he originally applied this 

 name to both these species as his successors have certainly done until 

 recently; and the synonomy "Schisoneura lanigera {americana in part, 

 of authors)," correctly designates the "rosette aphid" of the elm. 



There are apparently 3 summer generations of progeny of the 

 elm leaf migrants upon the apple in Maine, — two apterous gen- 

 erations followed by a generation part of which, the fall mi- 

 grants, become winged and leave the apple and part develop into 

 apterous forms and remaining on the apple give birth to nymphs 

 ■which while still young seek protection at the base of the tree 

 for the winter and are known as the hibernating nymphs. 



It is the function of the migrants to seek the winter host 

 and there give birth to the true sexes. These are the tiny yel- 

 lowish brown egg-laying females and the still smaller pale yel- 

 low males. Both sexes are wingless and with rudimentary 

 mouth parts which are apparently functionless. One compara- 

 tively large yellow egg occupies nearly the whole abdomen of 

 the female and with the deposition of this the cycle of the spe- 

 cies closes, — or begins. It is too complicated a performance to 

 follow easily but the outline on page 338 will be useful as a 

 summary. Such a cycle with the annual migration to and from 

 the apple with the elm serving as host for the first three spring 

 generations is undoubtedly typical for lanigera. The hibernat- 

 ing nymphs which remain protected about the crown of the 

 apple over winter and ascend to tender places on the bark before 

 feeding in the spring give what looks like a "closed cycle" of 

 apterous viviparous females persisting on the apple. How long 



f'Curling and gnarling the leaves of the White Elm (Ulmus ameri- 

 cana), forming thereby a sort of pseudo-gall. The curl made by a sin- 

 gle stem-mother in the spring takes the pretty constant form of a rather 

 wrinkled roll of one side of the young leaf, but according as there is 

 more than one stem-mother, or as several contiguous leaves are affected, 

 the deformation assumes various distorted shapes, sometimes involving 

 quite large masses of the leaves." 



