PROGRESS REPORT ON THE EUROPEAN CORN BORER 10l 
tative localities of the New England area. These counts, with excep- 
tions noted, were taken during the spring of each year in corn and 
weeds left in their natural position in the field. Less than 1 per 
cent of the overwintering larvae were parasitized, so this factor may 
be practically ignored. 
Table 31. — Winter mortality of Pyrausta nubilalis larvae in New England 
Winter period 
Total 
larvae 
counted 
Total 
larvae 
dead 
Per cent 
of larval 
mortality 
1919-20 ------ - - - - __-_--- 
1,231 
1,776 
2,478 
10, 100 
10, 989 . 
110 
133 
233 
838 
440 
8.9 
1920-21 - - - - 
7.5 
1921-22 - . _ _ . _ - _ - - _ - _ 
9.-4 
1922-23 
8.3 
1923-°4 [ ------ - - - - 
4.0 
Total ---------- - - -. - - - 
26, 574 
1,754 
i 
6.6 
1 
1 Limited to counts in experimental plats of corn. 
Table 31 shows that the average winter mortality for the period 
was 6.6 per cent. This figure applies to plants which were in a 
natural position; that is, plants which were standing erect, broken 
over, or lying upon the surface of the soil. When infested corn- 
stalks or other plant remnants are cut and gathered and placed 
in large piles during the fall and left in this condition all winter, 
a considerable proportion of larval mortality sometimes occurs in 
the interior of such piles when they are exposed to conditions of 
excessive moisture. It is not possible, however, definitely to at- 
tribute this killing to true winter mortality, because other influences, 
such as mechanical injury during handling or fermentation of the 
plant material may contribute to this result. In a recent publica- 
tion (5) Barber discusses the importance of winter mortality in 
the natural control of the European corn borer in New England. 
Comparative Winter Mortality According to Position of Host 
In the course of experiments carried on during the winter of 
1920-21, with the object of ascertaining the comparative winter 
mortality of larvae in cornstalks standing erect and cornstalks 
lying upon the surface of the soil, it was found that in the former 
the winter mortality was 1.5 per cent and in the latter 4.3 per cent. 
In cornstalks standing erect .there was no appreciable difference 
in the percentage of mortality between larvae inhabiting the lower 
and upper portions of the stalks. 
Comparative Winter Mortality According to Topographic Location of Host 
During the spring of 1921 counts for winter mortality were made 
in localities representing typical conditions of lowland areas, high- 
land areas, and coastal areas. These counts were all made in corn- 
stalks left in the field of the New England area under natural 
conditions. According to the figures obtained in these counts, the 
percentages of winter mortality on lowland areas, highland areas, 
and coastal areas were 19.9, 16, and 12.8 per cent, respectively. The 
average winter mortality for the New England area, including larvae 
from cornstalks and weeds, was 7.5 per cent during this period. 
