PROGRESS REPORT ON THE EUROPEAN CORN BORER 
55 
Table 13 shows that as a result of larval injury, when 100 per cent 
of the stalks were infested at harvest, an average of 16.7 per cent of 
these stalks were broken over below the ear and an average of 22.9 
per cent were broken over above the .ear, thus making a total average 
of 39.6 per cent of the stalks broken over at this time. The examina- 
tion of 188 ears borne by the 287 plants examined revealed an average 
of 78.2 per cent with infested ear stems and an average of 12.8 per 
cent of the ear stems broken over before harvest. 
LENGTH AND VOLUME OF TUNNEL IN STALK MADE BY EACH LARVA 
In order to obtain information relative to the length and volume 
of each tunnel bored out or consumed by each larva, measurements 
were made of individual tunnels in 35 stalks of sweet corn and in 6 
stalks of dent corn, each of which was inhabited by a single larva. 
Care was taken in the selection of these stalks to ascertain that each 
tunnel was made by the larva then inhabiting it. It was not possible 
in every instance, however, to determine whether the larva in its 
younger stages had or had not fed upon the exterior of the same or 
adjoining plants before starting its tunnel in the stalk. The results 
of these measurements are shown in Table 14. 
Table 14. — Length and volume of tunnel in stalk made by each European corn 
borer larva 
Type of corn 
Number 
of stalks 
Average 
length of 
each tunnel 
in inches 
Average 
volume of 
each stalk 
(cubic 
inches) 
Average 
volume of 
eachtunnel 
(cubic 
inches) 
Average 
per cent 
loss in 
volume to 
each stalk 
35 
6 
9.036 
6.125 
7.0441 
16. 5263 
0. 2492 
.1690 
3. 538 
Dent 
1.022 
8.610 
2.816 
From Table 14 it is seen that the average length of the tunnel 
made by each larva under observation equaled 8.61 inches, and that 
there was an average of 3.489 per cent loss in volume caused by the 
boring and feeding of each larva. 
EXTENT AND EFFECT OF BROKEN-OVER TASSELS 
Counts made in badly infested cornfields have shown as many as 
89.9 per cent of the tassels broken over. Many ears of corn from 
fields thus affected are abnormally small in size, or lacking in proper 
grain formation, even though the}^ are not directly injured by the 
larvae, but it has been difficult definitely to assign the lack of proper 
fertilization as a reason for this condition, because such ears are 
usually borne by plants which have been otherwise seriously injured 
by the insect. When the tassel breaks over early in its development 
there results a loss of pollen, but this type of injury or mutilation 
has been considered by corn technologists as unimportant, even where 
a large proportion of the tassels are thus affected. The remaining 
uninjured tassels are said to furnish sufficient pollen for the proper 
fertilization of the plants in the vicinity. The percentage of tassels 
broken over as a result of European corn borer injury during 1920 
and 1921 in certain fields of sweet, flint, dent, fodder, and pop corn, 
representing ord'nary conditions in the heavily infested portion of 
New England, is shown in Table 15. 
