134 
BULLETIN 1476, U. S. DEPARTMENT OE AGRICULTURE 
NATURAL ENEMIES 
Although a variety of natural enemies of the European corn borer 
have been recorded in this country, usually they do not attack the 
insect in any appreciable numbers and can not from present indi- 
cations be relied upon to hold it in check. 
The fact that the larvae normally feed within their hosts greatly 
reduces the opportunity for attack by parasitic and predacious 
enemies. The small larvae, however, are exposed to attack for a 
short time before entering the plant. This is true also for certain 
individuals of the larger larvae when feeding on or near the ex- 
terior of the plant, or when migrating to other parts of the same or 
adjacent plants, and when seeking shelter in unprotected locations. 
PARASITES 
NATIVE PARASITES 
In New England the small chalcid Trichogramma minutum 
Riley periodically parasitizes considerable numbers of Pyrausta 
nubilalis eggs, particularly those of the second generation in the 
latter part of the season. Toward the end of the summer of 1919 
an average of 43.5 per cent and a maximum of 75 per cent of the 
second-generation eggs were parasitized in 23 towns in representa- 
tive parts of the area where egg collections were made. In 1921 this 
species destroyed an average of 30.7 per cent, and a maximum of 
74 per cent of the second-generation eggs in 24 representative towns. 
This chalcid is apparently very variable, however, in occurrence 
from year to year, as in 1920 only 6.6 per cent of the second-genera- 
tion eggs were parasitized in this same area. Although the parasitism 
of the second-generation eggs was comparatively high during these 
two years, less than 1 per cent of the first-generation eggs were 
parasitized in this same area. In the New York areas of infestation 
no parasites have been found in any of the eggs collected. Table 43 
summarizes the results of egg collections in New England for 
parasitism by T. minutum from 1919 to 1921, inclusive. 
Table 43. — Parasitism of Pyrausta nubilalis eggs by Trichogramma minutum 
in New England, from 1919 to 1921, inclusive 
First generation 
Second generation 
Year 
Number 
of eggs 
collected 
Number 
of eggs 
para- 
sitized 
Per cent 
of para- 
satism 
Number 
of eggs 
collected 
Number 
of eggs 
para- 
sitized 
Per cent 
of para- 
sitism 
1919 . -. 
11, 384 
28,046 
15 
29 
266 
0.13 
.10 
.72 
28, 418 
53, 198 
79, 802 
12,948 
3,501 
23, 997 
45.5 
1920 
6.6 
1921 
Total 
36, 835 
30.1 
7fi 2fiS 
310 ! 161.418 
40. 446 
.406 
1 
25.05 
The fact that most of the parasitism by T. minutum is confined to 
the second-generation eggs, and particularly the eggs deposited dur- 
ing the late season, rather reduces the effectiveness of the species 
as a factor in preventing injury by its host. 
