Puant Lice InsgurInG FOLIAGE AND FRuIT OF THE APPLE 725 
of eggs. As a consequence no observations have been made on the failure 
of the eggs of this species to hatch due to the various factors which seem 
to play such a large part in the case of Aphis pomt. 
The stem mother 
The young, as soon as they hatch, actively seek out the opening buds 
of the apple, seeming to prefer the fruit buds. Under normal conditions 
close search has to be made for this species, as it usually occurs in very 
small numbers mingled among the abundant individuals of Aphis pomi and 
A. avenae. However, the whitish pulverulence, or powder, which covers its 
more or less dark purplish body readily serves as a distinguishing character. 
This pulverulent condition is especially marked after the second molt. 
The stem mothers of this species differ considerably in their habits 
from those of the other two common species of apple aphids. As soon 
as the buds open, this species is most commonly found congregated about 
the opening flower buds; into these they penetrate, frequently attacking 
the. flower stalks as the buds unfold. Some of the insects settle on the 
underside of the leaves, quickly causing them to curl. 
The severe curling of the foliage caused by this species is in all proba- 
bility the most characteristic feature of its work. A single stem mother 
located on the underside of a leaf near the midrib will cause the leaf to 
fold almost as tightly as the outer wrappings of a cigar (Plate XIV). 
As to the active agent which causes such a reaction on the part of the 
plant, scarcely anything is known. It requires the presence of only a 
few stem mothers to cause a severe curling of all the leaves surrounding 
an opening flower bud, and within such curls ideal protection is 
afforded to the rapidly developing plant lice. This work of curling the 
foliage so severely in the spring is due to this species alone; Aphis pomz 
causes only a partial folding, usually doing nomore than bringing the tip 
and the base of the leaf into contact and never producing a close curl. 
Furthermore, Aphis sorbi is rarely found attacking the young and rapidly 
growing shoots, restricting itself to the foliage, the flower stalks, and the 
young fruit. 
The stem mothers reach maturity at the time when the apple trees 
are coming into bloom. The blooming time varies from year to year, 
but in 1915 the first stem mothers became mature and began bringing 
forth young on May 10, just as the earliest blossoms were opening. In 
