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Transgenic Cotton for Insect Control


Transgenic Cotton for Insect Control Peter C. Ellsworth, Ph.D. IPM Specialist, University of Arizona Maricopa Agricultural Center Maricopa, AZ, USA – PowerPoint PPT presentation

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Title: Transgenic Cotton for Insect Control

Transgenic Cotton for Insect Control
  • Peter C. Ellsworth, Ph.D.
  • IPM Specialist, University of Arizona
  • Maricopa Agricultural Center
  • Maricopa, AZ, USA

  • 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

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

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
  • Safety (risks)
  • Resistance
  • Impact of gene on plant
  • Biodiversity
  • non-target effects

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

Bacillus thuringiensis (Bt)
  • Common soil bacterium
  • Present in nature in a variety of forms (species
  • 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

Bacillus thuringiensis (Bt)
  • Crystalline proteins are classified according to
    structure have a specific nomenclature (e.g.,
  • 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

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
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.
AZs Primary Lepidopteran Pest
  • Pink Bollworm
  • Multiple generations
  • Adult lays eggs on bolls or susceptible squares
  • Larvae hatch penetrate bolls within 24 hrs

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

Secondary Lepidopteran Pests
  • Occasional pests
  • Induced pests

Helicoverpa zea Heliothis virescens
Trichoplusia ni
Estigmene acrea (Arctiidae)
Bucculatrix thurberiella
Spodoptera exigua
Bt Cotton Questions
  • Efficacy economic studies
  • How effective is the gene?
  • Are oversprays required for lepidopteran control?
  • If so, are there new scouting threshold
  • 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
Search for
large larvae No unintended effects Yes,
actively growing No, some not marketed gt 98
(?) No unintended effects
BG Cotton Efficacy
  • Young larvae present regardless of cotton type
  • Little difference between Bt non-Bt (-)

BG Cotton Kills Small Larvae
  • PBW larvae must feed in order to be killed.
  • Large larvae survive mainly in non-Bt varieties.

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
  • 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

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

  • 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

High-Dose Strategy, Depends on
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.

Development of Additional Transgenes (Bts)
  • Bollgard II
  • 2 Bt gene product, original Bollgard (Cry1Ac)
  • 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

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

Isoline Studies of BG BGII
  • Replicated studies
  • Artificial natural PBW infestations
  • Sprayed Unsprayed conditions

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

Live 1st Instars
BGII Results - PBW, All Instars
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

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

Spectrum of Activity for BG (Cry1Ac)
Spectrum of Activity for BGII (Cry1Ac Cry2Ab)
High Dose and Efficacy?
  • Throughout our early work with BG cotton, we
    often would find low levels of survivors from
    our field plots

Source of Survivors
  • Low expression of Bt in plants?
  • Low levels of non-Bt contaminants?
  • In the seedbag
  • From volunteer seed
  • Resistance?

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
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.

Non-Target Organisms (NTO)
  • Over 370 arthropod species have been tracked in 2
    years of field studies using a variety of
  • 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.

  • 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
  • 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
  • Other than new Bt genes/events, there are few, if
    any, development plans for insect contol products.

  • All University of Arizona crop production crop
    protection information is available on our web
  • Arizona Crop Information Site (ACIS), at
  • http//