1924] Winter Mortality of the European Corn Borer 291 
map of Life Zones of the United States (1910-Check-List of 
North American Birds, 3d ed., rev.; also published in separate 
form, Biol. Survey, U. S. Dept. Agr.) the Boreal region is shown 
to extend southward into central New Hampshire in the shape of 
a long arm. It is interesting to note that the experiments placed 
in Bristol, N. H. in the fall of 1922 showed the following spring 
22 per cent of winter mortality and the material placed in the 
same location a year later and examined in April of 1924 showed 
winter mortality of 24 per cent. This town is located within the 
southern point of the boreal region referred to above and is the 
only locality that showed considerable winter mortality during 
each of the two years. Furthermore, the only other locality 
that showed a high percentage of mortality during the winter 
1923-1924 (Concord, N. H. with 39 per cent of mortality) lies 
just without the southern edge of this region. This is the only 
area in New England where infestation by this insect is known 
to approach the boreal zone as portrayed in the map referred to. 
The information is not sufficient to warrant a prediction as to 
whether this insect would thrive in the Boreal zone, but it may 
be highly suggestive of a condition that may eventually be 
found to exist. 
Summary. 
The studies recorded in this paper were undertaken to 
determine what importance winter mortality played in the 
natural control of the European corn borer in New England. 
Examinations of several host plants of this insect in the spring 
of 1922 and the spring of 1923 showed that mortality was greatest 
in pigweed {Amaranthus retroflexus L.) and barnyard grass {Ech- 
inochloa crusgalli (L.) Beauv.), the mortality in pigweed averag- 
ing 21 per cent in 1922 and 14 per cent in 1923, while in 
barnyard grass 10.9 per cent were found dead in 1922 and 
9.6 per cent perished in 1923. The average mortality in all host 
plants and localities was 9.4 per cent in 1922 and 8.3 per cent in 
1923. All of these examinations were made in the heavily in- 
fested area of the New England infestation, bounded by Marble- 
head, Mass., on the north, Arlington, Mass., on the west and 
Quincy, Mass., on the south. 
