Feb. 21, 1916 
Green Apple Aphis 
965 
higher than those normally occurring out of doors. Several lots of eggs 
containing “resting” embryos were taken into the greenhouse at 
Vienna, Va., during the winter of 1915. 1 The first lot was taken on 
January 7 and other lots were taken at intervals of from one to two 
weeks until after growth was resumed. All the eggs in all lots died 
within two weeks. Over 50 per cent of all eggs placed in the green¬ 
house after the revolution of the embryo commenced, hatched normally. 
It was at first thought that humidity might be a factor in this mor¬ 
tality, but the following experiment eliminated that. A very hairy twig 
which was well infested with eggs was cut in two. One half was placed 
in water, just as it was. The hairs acted as a wick, drawing the water 
to the top of the twig and keeping it and the eggs constantly moist. 
The base of the other twig was cleaned so that the water could not reach 
the hairs, and it consequently was dry. Both lots of eggs began to hatch 
on the same day. Moreover, hatching proceeded a little more rapidly 
on the dry than on the wet twig. It should be stated that the eggs used 
in this experiment had resumed growth before being taken into the 
greenhouse. These results are confirmed by the fact that no difficulty 
was experienced in hatching eggs taken into warm temperatures after 
the middle of March. 
It will be seen that the temperature effect upon the egg at this period 
is rather a complicated matter. The activities of the embryo in the spring 
are apparently initiated by a general rise in temperature above the 
normal winter average. It seems probable also that these higher average 
temperatures must continue for some time for this species, since warm 
weather of two or three days’ duration, occurring in January and Febru¬ 
ary, does not appear to induce any growth whatever in the embryo. 
Certainly there is no appreciable difference between embryos collected 
just before such a period and those collected after it. 
On the other hand, if the temperature affecting the eggs is artificially 
raised to greenhouse temperature (about 65° F.) at any time before the 
normal resumption of growth, the embryo dies. It is true that in certain 
instances some activity is induced, and embryos treated in this manner 
will be found to have developed somewhat, but in no case in these 
experiments did the revolution of the embryo occur. 
From data of the writers it would seem that the embryos need to pass 
through a period of cold weather, perhaps even need to be subjected to 
freezing temperatures. This is indicated by the fact that in eggs laid 
early in the season the embryos had reached the resting stage and ceased 
growth for three weeks or a month before later eggs were deposited. 
Yet these later eggs in their turn developed normally to the resting stage. 
The amount of low temperature needed by the insect is very uncertain. 
As suggested previously, it may be that a single freezing is sufficient, or 
1 The average temperature in the greenhouse was about 65® F. 
