102 BULLETIN 1476, TJ. S. DEPARTMENT OF AGRICULTURE 
Comparative Winter Mortality in Protected Situations 
Reference has previously been made to the habits of certain of 
the migrating larvae in seeking winter shelter by boring into va- 
rious wooden objects and by secreting themselves underneath rub- 
bish, clods of soil, loose bark of trees, and similar situations. In 
order to obtain information concerning the probable percentage of 
winter mortality among such larvae, a series of experiments were 
started during the late fall of 1919 in which large larvae were 
confined in cages containing soil, sawdust, dry manure, dry leaves, 
dry grass, moss, and wooden objects. Larvae were also confined 
in an empty wooden box. These cages were kept under a shelter, 
but otherwise they were exposed to winter conditions. A similar 
cage of infested cornstalks, kept under the same conditions, was 
used as a check. The average winter mortality in the test cages 
was 13.3 per cent and in the check cage 7.6 per cent. 
Comparative Winter Mortality in Different Species of Host Plants 
Table 32 shows the comparative winter mortality of the larvae 
in different species of host plants left in a natural position in the 
field during the winter of 1921-22 in the New England area. 
Table 32. — Comparative winter mortality of larvae of the European com bo?*er 
in different species of host plants during winter of 1921-22 in New England 
Host plant 
Number 
of locali- 
ties 
Number 
of larvae 
counted 
Total 
larvae 
dead 
Per cent 
winter 
mortality 
9 
5 
4 
2 
2 
2 
1 
901 
644 
273 
150 
210 
200 
100 
100 
33 
30 
4 
16 
42 
8 
11.0 
5.1 
10.9 
Polygonum _._ ..._ . __ 
2.6 
7.6 
21.0 
8.0 
Total . 
2,478 
233 
9.4 
According to the data shown in Table 32, there was some variation 
in the percentage of mortality in different host plants. No explana- 
tion can be given for the cause of this apparent variation. The 
mortality in the weeds in this series of experiments was 8.4 per cent, 
in comparison to a mortality of 11 per cent in corn. 
Larval Mortality When Frozen In Ice 
In order to determine the mortality of P. nuhilalis larvae con- 
tained in material frozen in ice, several series of experiments were 
performed in which infested cornstalks were placed in bodies of 
water during the late fall in such a position that they were subse- 
quently frozen in the ice. Examinations of the larvae contained in 
these stalks were made once a month during the period from Decem- 
ber to April, and it was found that the mortality for the first three 
months was practically equal to that of the check material left in a 
natural position. Beginning from about the 1st of March, however, 
the mortality of the larvae contained within the frozen-in stalks 
