PROGRESS REPORT ON THE EUROPEAN CORN BORER 103 
increased very rapidly. When the last series were examined during 
the first week of April less than 1 per cent of the larvae were alive. 
The heavy mortality occurred, therefore, during the period when 
the larvae would normally have become active preparatory to 
pupation. 
Winter Mortality of Larvae in Stored Material 
Jablonowski 9 has recommended, as a possible means of control to 
be applied to overwintering larvae, the storing of cornstalks in a 
comparatively weather-tight shed or barn until after the normal time 
for emergence of the moths the following spring. His idea is that 
the larvae contained in such stored material would be unable to 
complete their development when deprived, during the winter and 
early spring, of the moisture which is available to those larvae over- 
wintering in the normal locations and which is so essential for the 
completion of histolysis. 
The experiments which have been carried out up to the present 
time to determine the advisability of such a recommendation have 
shown that when larvae in stalks are stored in the insectary, or even 
more thoroughly inclosed structures for the winter season, a reduced 
percentage of them, ranging from 4 to 30 per cent, were able to 
complete their development, and that these were considerably re- 
tarded beyond the normal seasonal development that would be 
expected in the field. 
The percentage of larvae able to pupate and successfully emerge 
as adults was decreased when stored material was kept under heated, 
low-humidity conditions, such as those prevailing in a room of the 
laboratory. As will be discussed in a paper dealing with experiments 
upon the hibernation period, the cumulative effect of these various 
conditions of storing not only induces an immediate reaction re- 
flected by increased mortality and delayed pupation but also has 
the effect of delaying seasonal development during the subsequent 
growing season. In fact, only 9 per cent of the individuals which 
for two consecutive seasons had been denied the normal precipitation 
conditions during hibernation were able to develop the two genera- 
tions normally occurring in this area. 
Larvae without protection of cornstalks, ears, or similar covering 
seem unable to withstand either of the two conditions just discussed, 
and usually shrivel and dry up after the long exposure from fall 
to the following spring. 
PUPATION 
Pupation normally occurs within the tunnel made by the larva 
in its host plant. The larvae of the overwintering brood pupate in 
the tunnels which they have occupied during the winter, unless the 
condition of the host material in the spring is such that they are 
forced to migrate and seek similar but more suitable quarters free 
from extremes of moisture or desiccation. The summer-brood larvae 
normally pupate not far from the last feeding place in their tun- 
nels. Larvae of both broods may also pupate in protected places on 
the exterior of their host plant, such as between the silks on the ears 
of corn, between the leaf sheaths and the stalks, or between overlap- 
ping leaf blades of corn or other plants. Full-grown larvae which 
See footnote 1. 
