HATCHIXG OF GIPSY-MOTH EGGS. 11 
EFFECTIVENESS OF NONHATCH. 
Xonhatch as an agency in the natural control of the gipsy moth 
reaches the maximum of its importance in those sections of the in- 
fested area ^vhich have, some time during each winter, cold severe 
enough to kill all eggs exposed to its action. 
The principal protection from this killing cold is afforded by the 
snow; and the upper limit of this protection, measured from the 
ground, has been designated as the snow-protection line. It must 
not be supposed that this line has an}^ definite limits, for the depth 
of snow is an extremely variable factor. 
To determine the value of nonhatch as an agency in gipsy-moth 
control it is therefore necessary to determine the distribution of 
the egg clusters on the trees, the factors which influence this dis- 
tribution, and the proportion placed above the snow protection line. 
Fortunately a considerable amount of information along these very 
lines has been obtained during the progress of the " observation 
point " iuTestigations. 
The count of egg clusters made at each " point " was divided into 
two sections. The dividing line was m^arked at 5 feet from the 
ground on the trunks of the trees. The count of clusters above this 
line was known as the high count, of those below as the low count. 
Such a division was necessary on account of the work involved, 
which made impossible the complete counting of an entire point at 
one time. ' Many times also snow would prevent a low count but 
would not prevent the high count being taken. Five feet was chosen 
as a convenient point well above the usual snowfall. 
As the clusters were recorded with reference to their position above 
or below this 5-foot line, it will have to be the dividing line consid- 
ered in studying the distribution of clusters on the trees. A depth 
of snow to the extent of 5 feet is almost unknown in most sections 
of the gipsy-moth area, so we may safely consider that all the ex- 
posed egg clusters above 5 feet will be killed if the temperature drops 
to —20° F. or lower. At the same time there will probably be a 
considerable number of clusters between the 5-foot level and the 
top of the-snow during at least one period of severe cold, so that we 
are conservative in using the high count as a basis for figuring 
benefit derived from nonhatch. 
A careful consideration of the egg-cluster records from the 
" point '' notes, which were taken during seven consecutive years, 
shows that on the average 70 per cent of the clusters are laid above 
5 feet. An average of nearly 900 individual counts showed 72 per 
cent. 
The deposition of clusters is influenced largely by the ground 
conditions. If there is no underbrush and if debris, such as dead 
wood, bark, etc., is not present or if the ground is wet. most of the 
clusters will be well up on the trees. On the other hand, if debris 
is abundant, if there is much undergrowth, or if, as often happens 
in New England, there are stone walls running through the woods, 
a large proportion of the clusters will usually be found close to the 
ground. 
It is not possible to say just what causes the differences, but the 
" point '' notes show that they are as stated. In addition, the records 
