The Georgia Agricultural Experiment Stations
College of Agricultural and Environmental Sciences
The University of Georgia
Research Report Number 717
October 2008
Insect Screening Results
Evaluation of Insect Resistance in Commercial Corn Hybrids
Xinzhi Ni, Jeffrey P. Wilson, Brian T. Scully, and G. David Buntin
In 2008, 65 commercial hybrids were examined for insect resistance at Tifton,
Georgia. Fifteen of the 65 hybrids were new hybrids developed using new technology
(named YieldGard VecTran Triple, abbreviated as VT or VT3), which allows the stack of
multiple traits for stalk protection, root protection and weed control in one transformation
event. We have had a relatively dry corn growing season in 2008 which was favorable
for the rapid buildup of all insect populations in the irrigated experimental plots. Seven
ear-feeding insects were recorded as ear and kernel-feeding insect pests. They are in
the order of infestation severity: the corn earworm and the fall armyworm, the southern
green and brown stink bugs, the pink scavenger caterpillar and the sap beetles, and the
maize weevil. Disease surveys around flowering time showed that smut, southern rust,
and southern and northern blight infections were not a concern this year for all these
hybrids. All entries were planted on April 4, and harvested in the week of September 2,
2008. Plots were thinned to 20,000 plants per acre.
Total insect damage rating was based on ear-feeding insect (i.e., corn earworm and
fall armyworm) damage rating and percentage of damaged kernels caused by the stink
bugs, the pink scavenger caterpillar and the sap beetles, and the maize weevil. Overall
insect resistance rating used five categories; they were very good (VG), good (G), fair
(F), poor (P), and very poor (VP) as shown in the following table. While VG represents
the lowest amount of insect damage, VP represents the greatest amount of insect
damage. Losses to maize weevil, pink scavenger caterpillar and sap beetles were
based on damage by multiple generations of these insects as the crop matures in the
field. Corn earworm and fall armyworm damage was combined because the damage
was hard to be separated; pink scavenger and sap beetle damage also was evaluated
together. Corn earworm and fall armyworm feeding penetration in corn ears on the 65
hybrids was between 1.6 and 6.4 cm, which was higher than what we observed in 2007
(0.7 - 3.7 cm). It is worth noting that stink bug damage in 2008 (0.3-4.6% of discolored
kernels) was higher than in either 2006 (0-1.5%) or 2007 (0.02-2%). Other insect
damage was also higher in 2008 than in the previous two years. Pink scavenger
caterpillar and sap beetle damage was 0.4-7.6% in 2008 compared to 0.1-2.6% in 2007
and 0.1-3.2% in 2006, and maize weevil damage was 0.04-3.8% in 2008, compared to
0.1-0.8% in 2007 and 0-0.6% in 2006. The most significant insect damage was still
corn earworm and fall armyworm feeding on developing cobs, although increases in
other insect damage were recorded. Only 2 of 15 new transgenic hybrids developed
with VT or VT3 showed very good insect resistance, while 5 hybrids showed poor or
very poor insect damage ratings. The findings suggested insect resistance expressions
might vary among the hybrids. Timely harvest can substantially reduce losses caused
by these two insects. Rankings of the 65 hybrids for their resistance to the major earand kernel-feeding insects (i.e., corn earworm and fall armyworm, pink scavenger
caterpillar and sap beetles, maize weevil, and stink bugs) are given in the following
table. The lettered ratings in the table refer only to relative resistance to insects and are
not indicative of yield. Please refer to the yield data in other tests for specific
information.
During the damage evaluation in 2008, two physical features (i.e., husk tightness
and husk extension) of corn ears were examined. Husk tightness was assigned using a
scale of 1 to 5, in which 1 = very loose and 5 = very tight. Because average rating for
husk tightness ranged between 3.8 and 4.6, the ratings were further categorized into
three categories as loose (L), medium (M), and tight (T). Husk extension was shorter
compared to previous years, ranging between 1.2 and 7.3 cm. The insect damage was
not correlated to either of the husk features according to the data collected in 2008.
Hybrids resistant to insects are highly recommended for planting and are presently
the most economical means, especially in late plantings, for the reduction of ear-feeding
insect damage. Consult your local county agent and/or extension entomologists for
additional control recommendations for a specific insect pest in your region.
Data for this report were collected by J. C. Mullis (USDA-ARS, Tifton, GA),
Benjamin Berry, Justin Colbert, Cody Mauldin, and Austin Thompson (University of
Georgia, Tifton, Georgia).
Tifton, Georgia:
Evaluations of Corn Hybrids for Insect Resistance, 2008
Overall Resistance
to Insect Injury4
2 or more
years
2008
Hybrid Name1
Maturity2
Days to
Antheses
Husk
Extension
cm
Husk
Tightness3
DeKalb
Croplan Genetics
Pioneer
NK
Croplan Genetics
DKC69-71(RR2/YGCB)
851VT3
31N28(YGCB)
N77-P5CB/LL
8702RR
M
M
M
S
M
60
63
60
61
62
2.9
3.2
1.9
4
4.1
T
M
M
M
M
VG
VG
VG
VG
VG
G
G
G
G
G
DeKalb
Schillinger
Golden Acres
Croplan Genetics
AgraTech
DKC6640(YGCB)
EX5066
28Z89
9009RR
7754
M
M
M
M
M
59
62
61
61
60
3.5
6.5
3.5
5.5
6.6
M
L
M
T
L
VG
VG
VG
VG
VG
.
.
.
.
.
V5373 VT3
7891VT3
31P41
DKC66-23(RR2/YGCB)
DKC67-23(RR2/YGCB)
S
M
M
M
M
60
62
60
61
61
4.1
2.6
6.4
5.6
3.3
M
M
T
L
M
VG
G
G
G
G
.
.
G
.
G
AgraTech
Pioneer
Croplan Genetics
AgraTech
Greenwood
695RR
33M57(HX/LL/RR2)
7505VT3
1777
TL3450RR
S
S
S
M
M
61
62
59
61
61
4.5
3.2
5.8
4.8
4.1
M
M
M
L
M
G
G
G
G
G
G
G
GF
G+
Golden Acres
Croplan Genetics
Schillinger
Southern States
Croplan Genetics
2989RRB
6831RH
SX899
SS777VT3
8756RR/BT
M
S
M
M
M
64
60
61
61
62
2.2
3.6
5.6
4.6
2.7
M
M
M
M
T
G
G
G
G
G
G
G+
.
.
.
Croplan Genetics
Hytest
Hytest
Hytest
Hytest
6886VT3
87-65RR/BT
87-20RH
68-13RH
90-19RR
S
M
M
S
M
60
59
62
62
63
2.9
2.6
4.3
4
5.4
M
M
M
M
M
G
G
G
G
G
.
.
.
.
.
AgraTech
NK
DynaGro
DynaGro
Greenwood
EX8759
N78N-GT/CB/LL
58K81
V57YR82
EX3103RR
M
M
M
M
M
59
60
61
60
62
4.5
2.9
2.4
5
2.7
M
T
M
L
M
G
G
G
G
G
.
.
.
.
.
DynaGro
Pioneer
AgraTech
Pioneer
Pioneer
CXO 7319
31D58
797RR
33V16(RR2/YGCB)
31G65(RR2)
M
M
M
S
M
60
61
62
61
63
3.6
4.4
3.1
4.7
7.1
T
M
M
M
M
G
F
F
F
F
.
F
P
GF-
Company or
Brand Name
DynaGro
Hytest
Pioneer
DeKalb
DeKalb
Tifton, Georgia:
Evaluations of Corn Hybrids for Insect Resistance, 2008
(Continued)
Overall Resistance
to Insect Injury4
2 or more
years
2008
Hybrid Name1
Maturity2
Days to
Antheses
Husk
Extension
cm
Husk
Tightness3
DKC67-87(RR2/YGCB)
DKC69-40(VT3)
DKC6458(YGCB)
EX15133
SX896
M
M
S
M
M
61
59
59
61
63
4.3
3.9
4.5
7.3
2.2
M
M
M
M
M
F
F
F
F
F
.
.
.
.
.
NG6811
NG6834
68-68VT3
7550VT3
751CBLL
S
S
S
S
M
60
60
59
59
60
4.5
5.5
2.4
6.1
4.7
L
L
M
M
M
F
F
F
F
F
.
.
.
.
.
AgraTech
Garst
DynaGro
Greenwood
Southern States
EX8808
82R45GT
57V44
EX3280RR
SS731CL
M
M
S
M
S
61
59
60
62
61
5.2
2.6
4.7
2.4
3.9
M
M
M
M
M
F
F
F
F
P
.
.
.
.
P
Southern States
DeKalb
Schillinger
Fielder's Choice
Southern States
SS791CL
DKC61-69(VT3)
EX15135
NG6820
SS746VT3
M
S
S
M
S
63
60
62
59
62
1.6
3.6
5.4
1.2
3.2
M
M
M
M
M
P
P
P
P
P
.
.
.
.
.
Hytest
DynaGro
DynaGro
DeKalb
Croplan Genetics
82-12VT3
CXO 7119
V60YR82
DKC63-42(VT3)
8221VT3
M
M
M
S
M
62
62
63
59
62
1.9
2.9
1.9
2.1
1.6
M
T
T
L
T
P
P
P
VP
VP
.
.
.
.
.
Company or
Brand Name
DeKalb
DeKalb
DeKalb
Schillinger
Schillinger
Fielder's Choice Direct
Fielder's Choice Direct
Hytest
Hytest
AgraTech
All data in this table were collected from four replications.
1. The bolded entries have been examined for two or more years at Tifton, GA.
2. Maturity represents the hybrids categoried as short (S), medium (M), or long (L) season. Please note the
Days to Anthesis (or flowering) data at Tifton, GA did not always support the categorization though.
3. L = loose husks, M = medium-tight husks, T = tight husks;
4. Overall insect resistance to ear-feeding insects (i.e., the corn earworm and the fall armyworm, the stink bugs, the
pink scavenger caterpillar, and the maize weevil). Insect resistance measured by the ear-feeding insects from
a total of 20 ears (five ears per replication) per hybrid, where VG = very good, G = good, F = fair, P = poor, and
VP = very poor. The + and - signs for the average rating represent the inconsistancy among years.