178 MAINi; AGRICUIvTURAL EXPERIMENT STATION. I913. 



The elm leaf aphid which has been here under discussion as migrat- 

 ing to apple, mountain ash and hawthorn is the common elm leaf species 

 making a leaf cluster or "rosette" (Figs. 70 and 71) on the American 

 elm, composed of terminal leaves more or less bunched together. This 

 species is found in Maine, Missouri, Colorado, and doubtless all the way 

 between. Like other aphids it is fluctuating in its abundance, being 

 conspicuous everywhere some years and comparatively rare during 

 other seasons. 



Fig 67 shows a different type of leaf deformation common on elm 

 which is designated as "leaf curl" or "roll". Three different species 

 of aphids belonging to the same genus (Schisoneura) produce this 

 type of pseudogall in America.* One of these elm leaf curlers migrates 

 to apple ; another appears to be the English species which migrates to 

 the roots of currants and gooseberries ; and the destination of the 

 third is at present unknown. The second and third species will be 

 treated in further detail in a separate bulletin, this paper being con- 

 cerned only with the elm-apple aphids. 



Whether the leaf curler which migrates to apple is a distinct species 

 from the form which inhabits the rosette, I am not at present prepared 

 to state. The apterous viviparous generations have the same general 

 type of wax glands (Fig. '/2), the winged generations accord in char- 

 acters. 



It seems quite possible that under different conditions (as weather 

 or the size or position of the leaf attacked) that the same .species 

 might produce two types of elm leaf deformation. However that may 

 be it was Missouri migrants from such leaves as the one shown in Fig. 

 67 that gave me my first successful transfer test under control condi- 

 tions. 



Through the kindness of several southern entomologists, elm leaf 

 curl in considerable abundance with winged forms ready for migration 

 was secured in May, 1912, thus lengthening the season for purposes of 

 experimenting. These migrants, as previously explained (Science, Vol. 

 2,6, pp. 30-31), were caged over apple seedlings greenhouse-grown for 

 the purpose, the seeds having been planted in December 191 1 and Jan- 

 uary 1912. A few very successful colonies of woolly aphids were thus 

 established on apple seedlings by the progeny of the elm migrants, 

 the earliest of which was one started by migrants received May 12. 

 (Fig. 68). The fall migrants of this colony were mature and taking 

 flight September 20-23. 



So far as I am at present able to judge, the progeny of these migrants 

 from leaf curl and the progeny of migrants from rosette both look and 

 behave identically alike. Certainly if they prove to be distinct it will 



*Since Bulletin 203 went to press last year, significant collections 

 both from Maine and other parts of the country have come to my at- 

 tention which have added nuich to our knowledge of these species con- 

 cerning which much still remains to be learned. 



