240 MAINE AGRFCULTITRAL EXPERIMENT STATION. IQI2. 



t rosette (Fig. 462, when a group of terminal leaves are affected) 

 which they cause, producing the next generation, which are 

 also wingless. 



In the summer great numbers of winged individuals are de- 

 veloped. From the fact that Riley recorded 7 consecutive genera- 

 tions on elm and the occurence of what seems to be the elm 

 bark feeding generations of the same species (known as rileyi) 

 during the summer on tender elm bark, it would seem either 

 that the migration from the elm leaves of these summer migrants 



Fig. 442. Elm leaf curl, in which the alate spring migrants develop 

 before taking flight to apple bark. 



is partly to apple bark and partly to elm bark or that elm bark 

 colonies as well as leaf curl may be established by the first or 

 second apterous generations. Such a life cycle is indicated in 

 the accompanying table. This does not account for the genera- 

 tions resulting from the overwintering forms on the apple roots 

 as their sequence yet remains to be studied. The fall migration 

 of the woolly aphid from apple and the mountain ash I have 

 observed but I have not yet from observation linked it with the 

 true sexes on elm. That inference, however, from the evidence 

 of the spring migration to apple is unmistakable. 



There are still several important details to be worked out for 

 the woolly aphid of the apple and elm. Whether the elm bark 



