MAINE AGRICULTURAL EXPERIMENT STATION. 1 5 



progeny are the third generation and attain wings. These 

 winged aphids are known as the springs migrants and desert 

 the elm for the apple. 



It takes three weeks or slightly more or less, beginning about 

 the twentieth of June, for all the individuals of this third gen- 

 eration to get their growth so that the migration covers a con- 

 siderable period. The deserted rosette or leaf cluster at this 

 time looks like Fig. 58. During this time these winged aphids 

 may be found alighting on the leaves of apple, mountain ash, 

 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. 

 56, was on a mountain ash in Orono of which a record was 

 kept during the season of 191 2, at the Maine Agricultural 

 Experiment Station. 



Preventive and Remedial Measures. 



The foregoing account of the habits and characteristics of the 

 woolly aphid will suggest certain measures to control it. 



With the knowledge that the source of danger lies in the 

 migrants from the elm leaf, it is seen to be possible to control 

 the nursery stock by establishing nurseries at a safe distance 

 from susceptible elm trees or clearing out the elms from the 

 vicinity of large nurseries. As there are many places in the 

 country where the elm is not at all abundant this would often 

 be entirely practicable and where so would be the simplest and 

 most effective method of protection. As it is the seedling trees 

 that are most susceptible to injury and when attacked most 

 seriously damaged by ,the woolly aphid a method of protection 

 for the young trees while in the nursery is the most desirable. 



The raising of the elms and apples in the same nursery is thus 

 seen to be a hazardous proceeding and should be avoided. 



Again young orchards of clean stock set in parts of the coun- 

 try where the elm is not grown should be successfully protected 

 by excluding elms from the choice of shade trees. Indeed, the 

 matter of alternate hosts of the aphid enemies concerned should 

 always be borne in mind in planning the trees for an estate, and 



