Transgenic Cotton for Insect Control

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Transgenic Cotton for Insect Control

• Peter C. Ellsworth, Ph.D.
• IPM Specialist, University of Arizona
• Maricopa Agricultural Center
• Maricopa, 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

Recurrent back-crossing
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Spectrum of Activity for BG
Tobacco Budworm, the principal pest in the South
Trichoplusia ni
Spodoptera exigua
Heliothis virescens
Spodoptera frugiperda
Spodoptera ornithogalli
Pectinophora gossypiella
Bucculatrix thurberiella
Beneficial Insects
Pink Bollworm (PBW), our principal pest
Estigmene acrea
Helicoverpa zea (pre-bloom)
Agrotis Feltia spp.
Helicoverpa zea (post-bloom)
Pseudoplusia includens
Marmara spp.
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AZs 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
Trichoplusia ni
Estigmene acrea (Arctiidae)
Bucculatrix thurberiella
Spodoptera exigua
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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 growing No, some not marketed gt 98
(?) No unintended effects
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BG Cotton Efficacy

• Young larvae present regardless of cotton type
• Little difference between Bt non-Bt (-)
  varieties

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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, gt 6.8 sprays were made against PBW
  still, gt 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

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High-Dose Strategy, Depends on
Yes Yes?
Yes
Yes,
refuges No (?)

• The production of a dose high enough to kill
• gt99.9 of a susceptible (SS) population, and
• gt95 of the heterozygous (RS) individuals,
• A recessive resistance,
• Random mating,
• A low initial frequency of the R allele.

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Development of Additional Transgenes (Bts)

• 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

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Isoline Studies of BG BGII

• Replicated studies
• Artificial natural PBW infestations
• Sprayed Unsprayed conditions

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Warts are often formed at the site of PBW attack
Dead 1st instar in Bt cotton
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BGII Results - PBW, 1st Instars

• Dead 1st Instars

Live 1st Instars
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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

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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)

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Spectrum of Activity for BG (Cry1Ac)
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Spectrum of Activity for BGII (Cry1Ac Cry2Ab)
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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

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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 PBW
Before plants are tested for presence of Bt
After PBW from non-Bt plants are discarded
Cry1Ac 100
Cry2Ab 99.67
Both Genes 100
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Biodiversity / NTO Studies

• The reports of Bt effects on Monarch butterflies
  have fueled much emotional debate on the use of
  biotech crops.

• Monarch Butterfly, symbol of nature and
  wildness in North America.

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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
ACIS

• 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