PROGRESS REPORT ON THE EUROPEAN CORN BORER 105 
PROPORTION OF SEXES 
Table 33 gives data relative to the proportion of sexes as recorded 
from insectary reared material at Arlington,' Mass., during the 
period from 1918 to 1921. 
Table 33. — Proportion of sexes of Pyrausta nuoilalis at Arlington, Mass. {two 
generations) 
Generation 
Number 
of indi- 
viduals 
Per cent 
females 
Per cent 
males 
Second generation, 1917-18. 
First generation, 1918 
Second generation, 1919-20. 
First generation, 1920 
Second geneiation, 1920-21. 
First generation, 1921 
Total.... 
Average. 
342 
366 
221 
134 
933 
45 
2,041 |. 
49.5 
57.6 
37.0 
45. 5 
48.0 
51.2 
48.7 
50.5 
42.4 
63.0 
54. 5 
52.0 
48.8 
51.3 
Table 33 shows that of the individuals under observation during 
a three-year period at Arlington, Mass., the sexes occurred in about 
equal proportions, although in the spring brood the preponderance 
of males is marked. In each group under observation the males 
greatly outnumbered the females during the first part of the seasonal 
emergence period. 
Relative to the proportion of sexes in the one-generation areas, the 
adult emergence from 234 pupae collected at Scotia, N, Y., during 
the spring of 1920 consisted of 114 females, or 48.7 per cent; and. 
120 males, or 51.3 per cent. At Silver Creek, N. Y., notes were made 
upon the sex of 690 adults which emerged during the experimental 
work throughout the period 1921 to 1924. Of this number 350, or 
50.7 per cent, were females and 340, or 49.3 per cent, were males. 
At Sandusky, Ohio, 53.3 per cent of the adults emerging from experi- 
mental material during 1924 were females and 46.7 per cent were 
males. A total of 809 adults were included in this group. In each 
group under observation in these areas the males emerged sooner 
than the females in the proportion of nearly two to one, but as the 
emergence period advanced the females predominated in numbers. 
COPULATION 
Copulation usually occurs within a period of 12 hours after emer- 
gence from the pupa. During this act the male assumes a position to 
one side of the female and turns his abdomen at right angles with 
the body, meanwhile thrusting out the genital organs. When coition 
is successful, the male assumes a position directly to the rear of the 
female, the long axis of each being in a straight line. Three pairs 
of moths under observation remained in copula for an average period 
of 2 hours and 23 minutes. The moths have been observed in copula 
at nearly all hours of the day, but this usually occurs during the 
late afternoon and evening, at which time they are most active. 
