KIvM L.EAir CURL AiND WOOLLY APPLE APHID. 24I 



colonies are originated ty the stem mother, or by migrants from 

 the leaf curl or both; whether the mid June (in Maine) winged 

 forms from the elm bark colonies migrate to apple or scatter to 

 other elm bark, or both ; the significance of the difference in 

 antennal types of migrants from elm leaf curl (Figs. 451, 452, 

 454. and 458), whether indicating locality or conditional varia- 

 tion ; and complete sequence upon each food plant; — are subjects 

 for further study. 



These points can for the most part be watched only with 

 colonies upon seedling stock of the food plants in confinement 

 under such conditions that perfect control of the material can 

 be secured. While I have further work along these lines already 

 under way, some of the problems will need extended observa- 

 tions and it has seemed desirable not to wait until all tangles 

 are straightened out before j^ublishing the main fact of the 

 migration test from elm leaf curl to apple bark as this point has 

 an important bearing for young trees in nurseries and new 

 orchards and the economic significance of the migration data 

 will not, so far as can be anticipated, be influenced by further 

 detailed studv of the different generations. 



Thk Spring Migration. 



The fact of the migration from elm leaf to apple and moun- 

 tain ash under normal out of door conditions was established 

 during the summer of 1912. The migrants from the elm leaves 

 settle on the under side of the apple leaves of water shoots and 

 there produce nymphs v^diich seek the stem at leaf axils and 

 there congregate in woolly masses. The mountain ashes (Pyrns 

 americana and introduced species) are favorite summer hosts in 

 Maine. From one native mountain ash at Orono more than 

 400 such migrants were removed July 2 to July 12 from the 

 ventral surface of the leaves, and about 150 thriving clusters of 

 woolly aphid nymphs, the immediate progeny of these migrants, 

 were established on the shoots of this single tree.* 



In this connection it may be of interest to record a forced 

 migration test. On June 21, 1912, I placed several hundred elm 



* A more detailed account of this occurrence is to be published in 

 the October issue of the Journal of Economic Entomology. 



