PROGRESS REPORT OK THE EUROPEAN CORN BORER 
97 
Table 30. — Distribution of larvae of the European corn borer in cornstalks in 
Ohio during period from September 10 to November 3, 1924 
Larvae 
Larvae 
Larvae 
Larvae Larvae 
Larvae 
Larvae 
Larvae 
Larvae 
3 inches 
6 inches 
9 inches 
12 inches 15 inches 
18 inches 
21 inches 
24 inches 
27 inches 
and 
and 
and 
and 
and 
and 
and 
and 
and 
below 
below 
below 
below 
below 
below 
below 
below 
below 
Date of observation 
3 
(1924) 
OS 
S-H 
fs 
a 
PI 
S3 
u 
a 
S-. 
a 
d 
1-4 
"3 
'cS 
& 
P 
g 
g 
5 
g 
o 
,a 
o 
o 
£> 
o 
o 
O 
Eh 
^ 
Ph 
£ 
Ph 
3 
as 
Ph 
■3 
Ph 
3 
fc 
1 
Ph 
fc 
8 
Ph 
3 
Z 
Ph 
£ 
Ph 
fc 
Ph 
Sept. 10 to 16 
547 
16 
2.9 
40 
7.3 
61 
11. 1 91 
16.6 
108 
19.7 
124 
22.7 
140 
25. 6 
168 
30.7 
185 
33.8 
Sept. 17 to 25 
226 
10 
4.4 
23 
10.2 
26 
11. 5 46 
20.4 
53 
23.5 
67 
29.6 
68 
30.1 
85 
37.6 
95 
42.0 
Oct. 1 to 8 
173 
135 
110 
7 
7 
11 
4.0 
5.2 
10.0 
15 
23 
25 
8.7 
17.0 
22.7 
25 
36 
36 
14. 5 41 
26. 7\ 52 
32. 7 46 
23.7 
38.5 
41.8 
46 
67 
63 
26.6 
49.6 
57.2 
61 
81 
73 
35.3 
60.0 
66.4 
67 
85 
78 
38.7 
63.0 
70. 9 
78 
92 
82 
45.1 
68.2 
74.6 
95 
.54,9 
Oct. 23 
Nov. 3 
In general the percentage of total larval population present in the 
stalks up . to and including 18 inches from the ground increased 
approximately threefold between September 10 and November 3, 
and similar increases in larval population occurred in that por- 
tion of the stalks situated from 18 to 24 inches of the ground dur- 
ing this same period. (Table 30.) The high percentage of larvae 
present in that portion of the stalk up to and including 6 inches 
from the ground late in the season is also very impressive and serves 
to emphasize the necessity of cutting stalks low and as early in the 
season as possible. The greater proportion of the corn stubble in the 
machine-cut fields of Ohio and Michigan is at least 6 inches in height, 
while 24 inches is about the maximum height in fields cut by hand 
methods. 
POSSIBILITY OF SPRING FEEDING BY OVERWINTERING LARVAE 
In a previous publication (71) dealing with the habits of Pyrausta 
nubilalis larvae, reference has been made to the spring " feeding " 
of overwintering larvae. After a more detailed observation of 
the spring activities of the overwintering larvae, it appears that no 
real feeding occurs at this period and that the frass ejected from the 
larval burrows is composed of material which has been gnawed and 
cast aside during the process of preparing quarters for pupation. 
This frass is composed of rough angular particles, in contrast to 
the smooth, rounded pellets predominating in the normal excrement 
of actively feeding larvae. A histological study of the internal tract 
of overwintering larvae reveals an entire absence of solid food, and, 
furthermore, that important structural changes have occurred in the 
digestive tract of the larvae after active feeding ceased in the fall. 
The most important modification occurs in the ventriculus and 
rectum of the larva, and is of such a nature as to render these organs 
much more simple and less specialized in structure, the rectum losing 
for the most part its musculature. According to present knowledge, 
it appears improbable that overwintering larvae could successfully 
digest food or evacuate unassimilable matter in the spring. This 
conjecture is confirmed in a measure by inability to find larvae 
feeding on new growth in the spring, after they have passed through 
the winter. A spring examination of the digestive tracts of over- 
25411°— 27 7 
