10 LIFE HISTORY OF THE ALDER BLIGHT APHIS. 



of maples, on which return migrants from alders had delivered 

 themselves of the true sexes. 



These young stem-mothers, after hatching from winter eggs, travel 

 upward onto the branches and settle on the midrib of the underside 

 of the young leaflets. Usually there is but 1, though frequently there 

 may be 2, 3, or more on the same leaf, in consequence of which, as 

 well as from the increasing irritation, the leaves thus infested exhibit 

 a more or less marked tendency to fold or almost to " double up " 

 from the midrib downward. 



Under or within this protection or covering there may be observed 

 numbers of larvae and pupse of different stages, up to 100 or more, in 

 company with their mother, all of which, from early in June to the 

 end of July, or until the supply for migrants has been exhausted, 

 develop into winged migrants, without, however, leaving any larvae 

 behind to continue the series on the maple. These migrants fly then 

 to the alders, which frequently are rather distant from the maples, 

 and settle at once on the underside of the leaves of these shrubs, where 

 they are soon engaged in depositing their larvae, which surround 

 them in a circle of about 20 to 100. These larvae, after feeding for 

 about an hour or so, move to the twigs, branches, or stems of the 

 shrubs to start a new cycle of life for the species. Here a number 

 of generations is developed, after which, from about the middle of 

 September to the middle of October, numerous return migrants are 

 developed, which fly back to the trunks of the maples to continue the 

 cycle of life prescribed by nature. 



In consequence of these facts, which were gradually obtained, I 

 have been able to prove beyond a doubt that the original host plant 

 of this species is the silver maple, and not, as might be supposed, the 

 alder; the latter is its secondary food plant, and proof of this was 

 established during June of 1903. 



In conjunction with the above, it seems proper and just to give 

 some of the observations made through which the life history of the 

 species was definitely ascertained. 



Besides the migrants from the maple and return migrants from the 

 alder, I ascertained also that after the departure of the return 

 migrants numbers of mature, apterous females still remain upon the 

 alders and keep on producing additional larvae, all of which, without 

 casting a skin, crawl down the stems, and frequently to the stouter 

 roots, which are more or less surrounded by cavities made by ants, or 

 hide between or beneath the dead leaves, etc., which surround the base 

 of the shrubs, for hibernation. These form the first hibernating series 

 of larvae and neither feed nor grow until the sap rises again the follow- 

 ing spring, when, after an absorption of sufficient nourishment, they 

 cast their first skin and keep on growing until mature, at which time, 



