1924] 
Winter Mortality of European Corn Borer 
283 
Observations in the spring of 1923. 
Investigations of winter mortality during the spring of 
1923 were of two distinct sorts; first, observations of the winter 
mortality in host plants that had remained undisturbed through 
the winter and second, observations of the winter mortality in 
corn stalks placed in representative localities the previous fall 
for the purpose of obtaining information on this subject. 
In Table 2 the results of the observations of winter mortality 
in host plants that had remained undisturbed during the winter 
are shown. The highest rate of winter mortality was found in 
pigweed {Amaranthus retroflexus L.) and false ragweed (Iva 
xanthifolia Nutt.) ; the least mortality in prince’s feather {Poly- 
fonum orientale L.) and hemp {Cannabis sativa L.). These exa- 
minations were confined to localities within the heavily infested 
area of Massachusetts as were the corresponding observations 
of the preceding spring. The average winter mortality for all 
localities and host plants was found to be 8 . 3 per cent. 
In table 3 winter mortality is compared in corn stalks that 
had passed the winter in various conditions. Here mortality 
appears to have been highest in corn stubble and lowest in corn 
that was i)iled up in the fall and passed the winter in this condi- 
tion. 
TABLE No. 3. 
Winter mortality in corn stalks that passed the winter in 
SEVERAL CONDITIONS. 
Condition of 
corn stalks 
Num- 
ber of 
collec- 
tions 
Num- 
ber of 
locali- 
ties 
Total 
num- 
ber of 
larvae 
Num- 
ber of 
larvae 
dead 
Mean 
per 
cent 
of 
larvae 
dead 
Greatest 
winter 
mor- 
tality, in 
any col- 
lection 
Least 
winter 
mor- 
tality, in 
any col- 
lection 
Standing stalks 
Stalks lying on sur- 
25 
19 
2450 
186 
7.6% 
14% 
1% 
face of soil 
Stalks placed in piles 
12 
10 
1300 
101 
7.8% 
13% 
3% 
in the fall 
5 
3 
500 
26 
5.2% 
12% 
1% 
Corn stubble 
8 
6 
900 
100 
11.1% 
24.5% 
2% 
