Strains of field corn resistant to the survival of the European corn borer. Page: 4
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4 TECHNICAL BULLETFIN 823, U. S. DEPT. OF AGRICULTURE
hand-infested with 6 egg masses per plant, or about 180' eggs, in addition
to the natural infestation, which resulted in a mean of 1.6
mature borers per plant on the earlier planting made that year. In
1939 the hybrids and inbreds received 5 and 4 egg masses per plant
respectively, or about 150 and 120 eggs, in addition to the natural
infestation, which resulted in a total of 6.1 and 6.8 borers per plant,
respectively, from both sources of infestation. The mean number of
borers in the different strains of corn varied from these means for 4
reasons: (1) The later silking strains contained fewer borers because
of a lower rate of survival in plants in a less advanced stage of development
at time of borer hatching, (2) the moths laid more eggs onsome
strains than on others because some strains were taller than others,
(3) the strains differed in their inherent resistance or susceptibility
to the borer, and (4) the mean number recorded showed variability
because of sampling errors.
With reference to the first reason given, data from the 10 years
of study show that the rate of change in the borer population due to
differences in the stage of plant development depends on the level
of borer population. When the borer population in all the strains
tested averaged 1.4 borers per plant the number of borers in any one
strain decreased or increased C.06 borer from this average for each
day later or earlier than the average in silking. The value 0.06 was
found to increase by linear regression to 0.27 as the general average
increased from 1.4 to 5.5 borers per plant. To allow for the correlation
between borers and stag of plant development, the number of
borers predicted for any strain was the average number expected for
its date of silking calculated on the basis of the regression of the observed
numbers of borers on silking dates,
With reference to the second reason, no count was made of the
number of egg laid on the different strains, but the mean height of
the strains during the oviposition period was measured. The half of
the hybrid strains silking earliest in 1939 averaged 3.4 inches taller
at the time of moth flight than the half silking latest. Since plots
of tall corn tend to receive more eggs than plots of shorter corn,10
the earlier silking strains contained more borers because of the larger
numbers of naturally laid eggs as well as because of their more mature
stage of development. While the regression of the observed numbers
of borers on silking dates is not a direct express on of the function
of height, any possible effect of the number of eggs laid is excluded.
from the deviations of the observed numbers of borers from the
numbers predicted, owing to the relationship of height with stage of
development as measured by silking.
As a group, the hybrids containing less than the number predicted
for them in 1939 averaged within one-half inch as tall at the time of
moth flight as the hybrids containing more than the predicted number.
It is not probable, therefore, that the differences in height of
the strains and resulting differences in the numbers of eggs laid were
factors entering into the question of inherent resistance or susceptibility
of the hybrid strains in 1939. As a final test the deviations of
the observed from the predicted numbers of borers were compared
with the heights of the strains, resulting in the nonsignificant correltion
coefficient (r) of -0.0874.08771.
" PATCH, L. H. HEIGHT OF CORN AS A FACTOR IN EGO LAYINo BY THE EUROPEAN CORN BORER MOT IN
BRE ONB-oXRATION AREA. Jour. Agr. Res. 64 (9): 503-616, lus. 1942.
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Patch, L. H.; Holbert, J. R. & Everly, R. T. Strains of field corn resistant to the survival of the European corn borer., book, May 1942; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc3504/m1/4/: accessed December 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.