1924] Winter Mortality of European Corn Borer 279 
THE IMPORTANCE OF WINTER MORTALITY IN THE 
NATURAL CONTROL OF THE EUROPEAN CORN 
BORER IN NEW ENGLAND.i 
By George W. Barber. 
Cereal and Forage Insect Investigations, Bureau of Entomology, 
United States Department of Agriculture. 
Among the factors that limit the sf)read and occurrence of 
an injurious insect in numbers sufficient to cause injury to crops, 
the ability of a species to withstand the rigors of winter occupies 
an important place, particularly in colder climates. If an insect 
is unable to pass successfully through this troublesome period 
of the year, it probably will rarely become a pest of first im- 
portance, although by means of annual migration it may occur 
frequently in some numbers. Such a condition is found, for 
example, in the case of the corn earworm {Heliothis ohsoleta 
Fab.) which as far as our knowledge goes cannot successfully 
winter in New England or other northern sections of the United 
States. However, this insect appears nearly every summer in 
numbers ranging from a mere trace to serious abundance in such 
areas, and as the writer has shown, (Jour. Agri. Res. 1924, 
XXVII p. 65) it became a pest of importance in New England in 
1921. The accepted explanation of this phenomenon is that the 
moths of this insect migrate northward each spring and summer, 
arriving in larger numbers some years than in others, and in the 
case of favorable growing seasons, possibly pass through a 
partial second generation, in which case injury is most noticeable. 
It may happen in the case of another species that a large 
number of individuals may perish in the overwintering stage, 
more dying during severe winters than during mild winters. 
This too may result in the species becoming injurious during 
some seasons and unimportant during others following a high or 
low rate of mortality during the preceding winter. 
Investigations of the European corn borer (Pyrausta nu- 
^Contribution from the Bureau of Entomology, U. S. Department of 
Agriculture in cooperation with the Entomological Laboratory of the Bussey 
Institution, Harvard University, (Bussey Institution No. 242.) 
