Transgenic Cotton for Insect Control
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Transcript of Transgenic Cotton for Insect Control
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Transgenic Cotton for Insect Control
Peter C. Ellsworth, Ph.D.IPM Specialist, University of ArizonaMaricopa Agricultural CenterMaricopa, AZ, USA
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Disclosure• Those engaged in the dialog on biotechnology
should fully disclose their relationships and opinions “up front” so that audiences can consider the context.
• Partial support for my research comes from companies with interests in biotechnology.
• The balance of support comes from state and federal sources of competitively available public funds.
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Disclosure (continued)
• Biotechnology and its products are neither inherently good nor bad.
• The specific process and each of its products should be scientifically and independently evaluated.
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Transgenic Cotton for Insect Control
• What is available now & in the future?• Origin, identity & development• Insect target(s) in the U.S.• Efficacy & utility in the Arizona
system (benefits)• Safety (risks)
– Resistance– Impact of gene on plant– Biodiversity– non-target effects
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Products Available for Cotton Insect Control
• Only 1 ‘trans’-gene has been commercialized• Based on the crystalline protein produced by
Bacillus thuringiensis (Bt)• Developed by Monsanto as Bollgard® and
incorporated into commercial varieties by several cotton seed companies (e.g., Delta Pineland Co. & Stoneville Pedigreed Seed Co.)
• Sold in the U.S., Australia, Mexico, South Africa, India, China, Argentina, Indonesia
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Bacillus thuringiensis (Bt)• Common soil bacterium• Present in nature in a variety of
forms (species & strains)• Produces proteins that are toxic
to insects• Commonly used in garden sprays
& for commercial agriculture, including organic farming
• Extremely well-known toxin in terms of human health & environmental safety
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Bacillus thuringiensis (Bt)• Crystalline proteins are classified
according to structure & have a specific nomenclature (e.g., Cry1Ac)
• Cotton has been transformed with Cry1Ac (narrow spectrum; Lepidoptera only)
• Protein binds with receptors in the insect gut causing pores which perforate the midgut & lead to cell leakage & insect death
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The Transformation• The gene of interest is spliced
out of the bacterium using a vector, like Agrobacterium tumefasciens, & transferred to cotton cells grown in tissue culture
• The cells are grown into a plant & then, after testing, plants are back-crossed into commercial lines to make new varieties
Coker 312
Recurrent back-crossing
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Spectrum of Activity for BGExcellent Control
No Control
Heliothis virescens
Pectinophora gossypiella
Helicoverpa zea(pre-bloom)
Bucculatrix thurberiella
Spodoptera exigua
Estigmene acrea
Trichoplusia ni
Spodoptera frugiperdaSpodoptera ornithogalli
Pseudoplusia includens
Agrotis & Feltia spp.
Beneficial Insects
Helicoverpa zea(post-bloom)
Pink Bollworm (PBW), our principal pest
Tobacco Budworm, the principal pest in the South
Marmara spp.
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AZ’s Primary Lepidopteran Pest• Pink Bollworm• Multiple generations• Adult lays eggs on bolls
or susceptible squares (SS)
•Larvae hatch & penetrate bolls within 24 hrs
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Alternatives for PBW Control• Repeated, broad-spectrum
sprays are required to prevent moths from invading fields
• No effective larvicides or ovicides
• Biological controls are limited by the biology of this pest– Little impact of parasitoid or
predators• Cultural controls can be very
effective– Requires early termination &
areawide compliance with plowdown requirements
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Secondary Lepidopteran Pests• Occasional pests
• Induced pests
Helicoverpa zea
Heliothis virescens
Estigmene acrea (Arctiidae)Trichoplusia ni
Spodoptera exigua Bucculatrix thurberiella
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Bt Cotton Questions• Efficacy & economic studies
– How effective is the gene?– Are oversprays required for lepidopteran control?– If so, are there new scouting & threshold
considerations?• Agronomic studies
– Impacts (+/-) on yield & fiber qualities?• Product integrity & stability studies
– High-dose through life of plant?– High-dose in all varieties?– Purity?
• Ecological studies– Impact on non-target organisms (NTO)
Ca. 100% for PBW
Not for PBW
Search for large larvae
No unintended effects
Yes, actively growingNo, some not marketed> 98% (?)
No unintended effects
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1
2
3
4
E
19-Sep 12-Oct
0102030405060708090
100
Infe
sted
Bol
ls (%
)
- BG - BG
19-Sep 12-Oct
- BG - BG
19-Sep 12-Oct
- BG - BG
19-Sep 12-Oct
- BG - BG
BG Cotton Efficacy• Young larvae present regardless of cotton type• Little difference between Bt & non-Bt (-) varieties
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1
2
3
4
E
19-Sep 12-Oct
0102030405060708090
100
Infe
sted
Bol
ls (%
)
- BG - BG
19-Sep 12-Oct
- BG - BG
19-Sep 12-Oct
- BG - BG
19-Sep 12-Oct
- BG - BG
BG Cotton Kills Small Larvae• PBW larvae must feed in order to be killed.• Large larvae survive mainly in non-Bt varieties.
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Impact on Arizona Cotton• In 1990, > 6.8 sprays were made against PBW; still, >
5% yield loss• Since 1996 when Bt cotton was introduced, it has
never required oversprays for PBW control, AND• Since 1997, only 0.5 sprays have been made against
PBW over all cotton acreage (Bt and non-Bt); i.e., an areawide reduction of PBW has occurred
• The net reduction in insecticide use has resulted in huge savings to farmers, and large improvements to the agroecosystem in terms of beneficial insect communities & IPM
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Safety - Resistance• Given time & exposure, insects
have the capacity to overcome most insecticides. Bt cotton may be no different, however, there are safeguards:
• Refugia• High-Dose Strategy• Development of additional
proteins
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Refugia• Objective: provide harborage for susceptible moth production
to reduce the chance of resistant (R) moths mating with each other
• U.S. growers are required to plant a proportion of their acreage to non-Bt cotton– 5% Refuge, if no lepidopteran-active insecticides are used on it, or else– 20% Refuge
RR RR RR SS
RRRS SS
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High-Dose Strategy, Depends on:
• The production of a dose high enough to kill: >99.9% of a susceptible (SS) population, and >95% of the heterozygous (RS) individuals,
• A recessive resistance,
• Random mating,
• A low initial frequency of the ‘R’ allele.
YesYes?
Yes
Yes, *refuges
No (?)
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Development of Additional Transgenes (Bt’s)
• Bollgard II®– 2 Bt gene product, original Bollgard (Cry1Ac) +
Cry2Ab– Final stages of US-EPA approval– Limited commercial production in 2003– Full replacement of BG varieties by 2008?
• Bollgard III– Little information on this available at this time;
research stages only• Cry1F
– Under development by Dow Agrosciences in combination with Cry1Ac
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Impact of Gene on Plant• Isogenic lines were developed for testing the
impact of the gene(s) on agronomic and efficacy characteristics of the plant
C312B
DP50 DP50B(Cry1Ac)
DP50
Cry1Ac Cry2Ab
DP50II(Cry1AC+Cry2Ab)
Particle gun Lines1. Cry1Ac+
Cry2Ab
2. Cry1Ac only
3. Cry2Ab only
4. Null
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Isoline Studies of BG & BGII• Replicated studies• Artificial & natural
PBW infestations• Sprayed & Unsprayed
conditions
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Dead 1st instar in Bt cotton
Warts are often formed at the site of PBW attack
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BGII Results - PBW, 1st Instars
50 50B 50BII0
1
2
3
4
5
50 50B 50BII0
1
2
Pink
Bol
lwor
m p
er b
oll 1st live
1st dead2nd live2nd dead
3rd live3rd dead
4th live4th dead
PupaeExits
Dead 1st Instars
Live 1st Instars
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Ellsworth/UA50 50B 50BII
0
1
2
3
4
5
50 50B 50BII0
1
2
Pink
Bol
lwor
m p
er b
oll 1st live
1st dead2nd live2nd dead
3rd live3rd dead
4th live4th dead
PupaeExits
BGII Results - PBW, All Instars
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BGII Results - B. thurberiella• BGII prevented cotton
leafperforator development better than BG
• Leaves at top of plant (younger) express highest doses of Bt
• Older leaves (bottom) have reduced doses of Bt
DP50BII DP50B DP500
10
20
30
40
50
CLP
Min
es p
er le
af
Bottom Middle Top
a
bc
a
bc
a
b b
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Marmara sp.• Citrus Peel Miner is an incidental
lepidopteran that mines the main stem and boll surfaces
• Cry2Ab alone (‘X’) is more effective than Cry1Ac (‘B’)
(-) (-) B BII 50 50B 50B 50X 50BII0
2
4
6
8
10Citrus Peel Miner Presence (per 10 plants)
NL Sa
bb
a a
b b
cc
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Spectrum of Activity for BG (Cry1Ac)
Excellent Control
No Control
Heliothis virescensPectinophora gossypiella
Helicoverpa zea
Bucculatrix thurberiella
Spodoptera exigua
Estigmene acreaTrichoplusia ni
Spodoptera frugiperdaSpodoptera ornithogalli
Pseudoplusia includens
Agrotis & Feltia spp.
Beneficial Insects
Marmara spp.
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Spectrum of Activity for BGII (Cry1Ac + Cry2Ab)
Excellent Control
No Control
Heliothis virescensPectinophora gossypiella
Helicoverpa zea
Bucculatrix thurberiella
Spodoptera exigua
Estigmene acreaTrichoplusia ni
Spodoptera frugiperdaSpodoptera ornithogalli
Pseudoplusia includens
Agrotis & Feltia spp.
Beneficial Insects
Marmara spp.
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High Dose and % Efficacy?• Throughout our early work with BG cotton, we
often would find low levels of “survivors” from our field plots
12-Aug 31-Aug 11-Oct
0102030405060708090
100
Infe
sted
Bol
ls (%
)
- BG - BG - BG1st
2nd
3rd
4th
Exits
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Source of Survivors• Low expression of Bt in
plants?• Low levels of non-Bt
contaminants?– In the seedbag– From volunteer seed
• Resistance?
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% Efficacy Against PBWCry1Ac Cry2Ab Variety
+ - DP50B- + 985X+ + 985BX+ - DP33B+ - DP448B+ - DP458BR+ + DP33BX+ - SG215BR- + SG125X+ + SG125BX
Raw*100
99.59199.324100
99.78899.536100100
99.256100
Adjusted100
99.591100100100100100100
99.758100
Cry1Ac 100%
Cry2Ab 99.67%
Both Genes 100%
Before plants are tested for presence of Bt
After PBW from non-Bt plants are discarded
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Biodiversity / NTO Studies
• Monarch Butterfly, symbol of nature and “wildness” in North America.
• The reports of Bt effects on Monarch butterflies have fueled much emotional debate on the use of biotech crops.
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Non-Target Organisms (NTO)• Over 370 arthropod species have been tracked in 2
years of field studies using a variety of methodologies.
• So far, no major or functional differences have been found in Arizona between BG, BGII, and conventional cotton communities…
• Except where harsh PBW sprays are needed in conventional cottons.
• Thus, Bt cotton ecosystems are not only safe, but safer than conventional cotton ecosystems where insecticidal inputs are higher.
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Conclusions• The use of Bt cottons in Arizona has provided the first
larvicidal and selective approach to controlling PBW.• The control provided by Bt cottons approaches
immunity. No survivors have been found in field studies.• Bt cotton has revolutionized our ability to implement IPM
in AZ cotton & reduced our insecticide inputs by over 60%.
• Future transgenic products for insect control in cotton should be independently & scientifically tested.
• Other than new Bt genes/events, there are few, if any, development plans for insect contol products.
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Information• All University of Arizona
crop production & crop protection information is available on our web site,
• Arizona Crop Information Site (ACIS), at
• http://ag.arizona.edu/crops
ACIS