Occurrence and Ear Damage of Helicoverpa zea on Transgenic Bacillus thuringiensis Maize in the Field in Texas, U.S. and Its Susceptibility to Vip3A Protein

1. VINODAKUMARGOUD

2. Occurrence and Ear Damage of Helicoverpa zea on Transgenic
Bacillus thuringiensis Maize in the Field in Texas, U.S. and Its
Susceptibility to Vip3A Protein
P-2019

3. Outline of Presentation
1. Introduction
2. Materials and Methods
3. Result and Discussions
4. Strategies can be used to prevent development of an Resistance
5. Conclusion

4. • Corn ear worm, Helicoverpa zea is major pest of Bt maize and cotton in the US.
• Cry1 and Cry2 Bt plants efficacy has been reduced against H.zea
• Earlier study showed, H.zea evolved 9.3 fold resistance to Vip3A.(Yang et al.)
• At present Vip3A is the only effective protein for H.zea in the US.
• From 1996 to 2005 field evolved practical resistance to Bt crops was only
reported in three cases.
• However, Cumulative number of cases of field evolved practical resistance to
transgenic Bt crops reached by 2018 is 19 crops.
INTRODUCTION

5. 1. Field Testing 2. Dose response bioassay (Diet overlay Bioassay) 3. Cotton leaf tissue bioassay.
Selected 5 Maize Hybrids; two are Non-Bt Hybrids and three Bt Hybrids.
A field trial was conducted on the Texas A&M University Farm in Texas on 26 March 2018.
Plots were arranged in RCBD with four plots for each maize hybrid.
In each plot, 20 plants per row were randomly sampled. Observations were made on the following
Bt Hybrids Non-Bt Hybrids
1. VT2P (Cry1A.105+Cry2Ab2)
(Monsanto Company, St. Louis, MO, USA)
1. DKC 67-70RR
(Monsanto Company, St. Louis, MO, USA)
2. INTRASECT (Cry1Ab+Cry1F)
(Pioneer Hi-Bred, Johnson, IA, USA)
2. P1637R
(Pioneer Hi-Bred, Johnson, IA, USA)
3. LEPTRA (Cry1Ab+Cry1F+Vip3A)
(Pioneer Hi-Bred, Johnson, IA, USA)
 percentage of plants with damaged ears  larval development
 percentage of plants with live larvae  area of kernel damage
 number of larvae per ear
Practical field evolved resistance evaluated in Three methods
1. Field Testing

6. Table 1. Plant injury and occurrence of Helicoverpa zea on different hybrids of N-Bt and Bt maize .
. in the field *

7. Two insect populations which are used for Diet overlay bioassay
The Vip3Aa51 protein provided by the BASF Company in a Soln. at Conc. of 2.9mg/mL
Each Bioassay consisted of seven concentrations, ranging from 0 to 3.16µg/cm2
Repeater pipette are used to put 0.8ml/well of liquid diet into 128 wells bioassay trays,
Once diet cooled and solidified; a volume of 40µl of Vip3A protein overlaid on to the diet surface in each
well.
After larval inoculation wells are covered with ventral tray lids.
Each Vip3Aa51 protein concentration;16 larvae/replication were replicated 4 times.
Larval mortality and weight were recorded after 7th day of inoculation.
Resistant Population to Cry Proteins Slowly Getting over Resistance to Vip3A Protein
Cry1F+Cry1A.105+Cry2ab2
(CEW-TX-VT3P-2018)
Cry1Ab+Cry1F+Vip3A
(CEW-TX-Leptra-2018)
2. Dose Response Bioassay (Diet Overlay Bioassay)

8. Table 2. The mortality response (LC50) of different populations of Helicoverpa zea
. to Vip3Aa51 protein in diet-overlay bioassays.

9. Mortality Response
LC50 for Cry popln
LC50 for Vip3A popln.
Vip3A Protein
(Cry1F+Cry1A.105+Cry2ab2)
(Cry1Ab+Cry1F+Vip3A)

10. Growth Inhibition Response
Vip3A Protein
(Cry1F+Cry1A.105+Cry2ab2)
(Cry1Ab+Cry1F+Vip3A)

11. • The performance of F1 Neonates Helicoverpa zea
• Were examined on the Non-Bt and Bt
3. Cotton Leaf Tissue Bioassay
Slowely Getting over Resistance to Vip3A Protein
(Population collected from the maize field)
Laboratory Susceptible Population
(Collected from the LSU Research station Parish)
Cry1Ab+Cry1F+Vip3A Susceptible population
Widestrike3 Non-Bt
Cry1Ac+Cry1F+Vip3A PHY 425RF
Bio-assy tray

12. Table 3. The performance of two different populations of Helicoverpa zea on cotton leaf
tissues *

13. Strategies can be used to prevent development of an Resistance
1. Follow of Refuge Methods (20%)
A. Structured refuge (Growing Non-Bt as Border crop)
B. Seed Blend (Incorporating Non-Bt Seed [refuge] with Bt seed in the same bag)
C. Natural refuge (Growing wild hosts or weeds hosts as border crop)
2. Pyramiding of genes (When one Bt Protein in pyramids is ineffective, remaining Bt protein can
. kill the insects)
3. Using different Bt-PIPs (Bt-Plant Incorporated Protectants) traits.
(In maize, 1st year Cry1F+Cry1A.105+Cry2ab2 and 2nd year Cry1Ab+Cry1F+Vip3A)
4. Planting a non-PIPs (Non-Bt) varieties if pest pressure is low.
5. Crop rotation break the pest life cycles.

14. Conclusion
 Data generated from this study clearly shows that H.zea has developed a practical
resistance to Bt maize plants expressing Cry1 and Cry2 proteins in Texas.
 Detected a high infestation of H.zea on Cry1Ab+Cry1F+Vip3A maize in the field.
 This is the first study to detect a high infestation of H.zea on Bt maize expressing
Vip3A protein in the field in the U.S.
 The results generated from this study provided a valuable information for promoting the
sustainable use of Vip3A technology for the control of H.zea and improving insect
resistance management strategies.

15. THANK YOU