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Entomological Investigations
Observations to determine average length, ear diameter, and degrees of
earworm (IHeliothis zea (Boddie) and/or Laphygma frugiperda (J. E. Smith))
damage and weevil damage among the varieties were made front January 20 to
January 23, 1964, following open storage after harvest. Most weevil damage
was caused by the rice weevil (Sitophilus oryzae (Linnaeus)). Five repre-
sentative ears from each plot were measured to the nearest 0.5 centimeter for
ear diameter and ear length. All available ears from each plot up to a maximum
of 25 ears per plot were each assigned an index number (0-5) to indicate the
degree of injury by earworms. An average plot index was computed and multiplied
by 100. The highest possible index, 500, would indicate the greatest assignable
degree of earworm damage. The following indexing system was used:
Index Fraction of Length of Ear Damaged
0 No damage
1 One-eighth or less
2 One-eighth to one-fourth
3 One-fourth to three-eighths
4 Three-eighths to one-half
5 One-half or greater
To evaluate the damage by weevils, 100 kernels were taken randomly from each
plot after the corn was shelled to count the number damaged.
The results of Test 1 are shown in Tables 7 and 8, those of Test 2 in Tables
9 and 10 and those of the white tropical field corn variety test are in Tables
11 and 12.
There were no significant differences among the varieties in Test 1 in
respect to either earworm or weevil damage.
In test 2, both earworm damage and weevil damage were highly significantly
greater among the DeKalb varieties than among the other varieties. Poey T-65
had highly significantly more weevil damage than Poey T-66. If one could assume
no effect from reciprocity of crossing, inbred "0" is a better contributor of
weevil damage resistance than inbred "R" when combined with inbreds "A", "S",
and "P". Poey T-62 suffered significantly less earworm damage than that
occurring anong Poey T-65 and T-66. This might imply that inbred "T" is relatively
an effective contributor of earworm resistance among these varieties.
In the test on white tropical field corn varieties, Rocamex H-505 received
significantly more earworm damage than Rocamex H-507. The genetical implication
here seems to be that "T1- x T is a better parent than "T for transmitting
earwom resistance. The larwom damage among Rocamex H-501 rd H-502 was
significantly less than that among Rocanex H-503, H-504, H-505, and H-507.
There are no obvious genetical implications. Earworm damage was significantly
less among Rocamex H-503 and H-504 than anong Rocanex H-505 and H-507. Inbred
lines "6", "7", "8", and "9" occurred among H-503 and H-504 whereas "10", "ll"
and "12" occurred among H-505 and H-507. When grouped, the Rocamex varieties
received highly significantly more earworm damage than the Poey varieties and