ELM LEAF ROSETTE AND WOOLLY APHID Otf APPLE. 333 



and hawthorn. They creep to the under side of the leaf and 

 remain there while they give birth to their progeny (i. e., the 

 fourth generation). These young, before they feed at all, crawl 

 to the stem of the water-shoots, or to some tender place on the 

 bark often near a pruning wound, and there start the colony on 

 the summer host plant. Such a young colony shown in Fig. 

 67, was on a mountain ash in Orono of which I kept a record 

 during the season of 1912. 



The main trunk of this tree was dead nearly to the ground, but 12 

 vigorous shoots had grown up measuring about 5 feet each. On June 

 28 this mountain ash had about 150 woolly masses of nymphs grouped on 

 the stem at the leaf axils. These nymphs ranged from very tiny ones 

 to half grown insects, none being mature at that date. One such woolly 

 mass contained 155 individuals of various sizes. (See Fig. 67). On 

 the ventral surfaces of the leaves of this mountain ash were stationed 

 many elm leaf migrants producing there their broods of nymphs which 

 could be seen, with the hand lens, to be augmenting the woolly masses 

 on the stem. Collections of these migrants thus stationed were made as 

 follows: July 2, 88 migrants; July 3, 211 migrants; July 5, 92 migrants; 

 July 8, 54 migrants; July 9, 80 migrants; July 10, 33 migrants; July n, 

 14 migrants ; July 12, 3 migrants. Only living individuals were collected, 

 dead ones being brushed off and discarded in the counts. Microscopic 

 examination showed them to be identical with winged forms collected 

 in elm leaf. Two large elm trees with leaves well stocked with this 

 species stood about a rod distant.* 



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

 test. On June 21, 1912, I placed several hundred elm leaf migrants at 

 the base of water shoots of an uninfested mountain ash on the Campus. 

 As the migrants are much more docile about sundown than earlier in the 

 day this was done about 7 P. M. They moved but little, most of them 

 creeping to the ventral side of a leaf and remaining there; and during 

 the night producing nymphs which sought the leaf axils of the water 

 shoots so that by the afternoon of June 22, the tiny nymphs had already 

 fed enough and secreted enough white wax to give the typical "woolly" 

 appearance to the young colonies. These and the progeny thrived on the 

 mountain ash in a perfectly normal way. 



On June 17, 1913, a laboratory cage check was started with migrants 

 from an elm rosette. The winged forms ready to desert the elm lea\es 

 were caged with a seedling mountain ash. Their progeny settled in 

 woolly masses on the stem of the seedling and are shown in Fig. 58. 

 By July 2 these had matured and were producing young which in turn 

 had matured and were producing nymphs on July 26. This third moun- 

 tain ash generation (sixth generation beginning with the stem mother) 



*Previously recorded in Journal of Economic Entomology, Vol 5, 

 No. 5, 1912. 



