1
Sharlene
R.
Matten,
Ph.
D.,
Biologist
USEPA/
OPP
Biopesticides
and
Pollution
Prevention
Division
Matten.
sharlene@
epa.
gov
703­
605­
0514
Sharlene
R.
Matten,
Ph.
D.,
Biologist
USEPA/
OPP
Biopesticides
and
Pollution
Prevention
Division
Matten.
sharlene@
epa.
gov
703­
605­
0514
WideStrike
(
Cry1F
+
Cry1Ac)
Cotton:

Issues
Related
to
Establishing
an
IRM
Plan
2
Purpose

Present
various
aspects
of
EPA's
analysis
of
Dow's
WideStrike
cotton
IRM
submissions

Dose
studies
for
Heliothis
virescens
(
TBW,
tobacco
budworm),
Helicoverpa
zea
(
CBW,
cotton
bollworm),
and
Pectinophora
gossypiella
(
PBW,

pink
bollworm)


Pest
adaptation
likelihood
including
modeling
and
IRM
Plan

EPA
will
decide
on
the
acceptability
of
Dow's
WideStrike
IRM
Plan.
3
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
4
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
5
Key
IRM
Issues
for
SAP

Dose

Cross­
resistance
potential
(
Cry1F
and
Cry1Ac)


Cotton
bollworm
alternate
hosts

Models
 
tobacco
budworm
and
cotton
bollworm

IRM
Plan
6
Outline

Key
IRM
issues

What
is
WideStrike
cotton?


Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
7
What
is
WideStrike
Cotton?


Event
281­
24­
236
(
Cry1F))
X
Event
3006­
210­

23
(
Cry1Ac)

=
Event
281­
24­
236/
3006­
210­
23

WideStrike
expresses
both
Cry1Ac
and
Cry1F

Cry1Ac
expressed
in
BollgardTM
cotton
and
BollgardTM
II
­
Cry1Ac
+
Cry2Ab

Cry1F
expressed
in
HerculexTM
corn
8
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
9
Key
Lepidopteran
Pests
of
Cotton

Major
pests:


tobacco
budworm
(
Heliothis
virescens,
TBW)


cotton
bollworm
(
Helicoverpa
zea,
CBW)


pink
bollworm
(
Pectinophora
gossypiella,
PBW)


Secondary
pests:


cabbage
looper
(
Trichoplusia
ni,
CL)


soybean
looper
(
Pseudoplusia
includens,
SL)


beet
armyworm
(
Spodoptera
exigua,
BAW)


fall
armyworm
(
Spodoptera
frugiperda,
FAW)


southern
armyworm
(
Spodoptera
eridania,
SAW)
10
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
11
Factors
in
Pest
Adaptation

Operational
factors

Biological
factors

Genetic
factors

IRM
Plan
must
consider
all
factors
12
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
13
Operational
Factors

Mode
of
action

Target

Larval
effects

No
adult
effects
 
no
insecticidal
crystal
proteins
(
ICPs)
expressed
in
nectar

Dose
and
functional
dominance

Pyramided
Toxins

Cry1F
+
Cry1Ac

Market
share
14
(
Bravo,
2004)
15
Cry1Ac
and
Cry1F
Expression
N.
D.,
<
LOQ,
0.17
0.51,
0.54,
0.88
Roots
(
defoliated,

pollination,
seedling)
0.64
3.52
Bolls
N.
D.

1.45
1.83
1.82
1.31
1.82
Cry1Ac
Mean
Expression
(
ng
ICP/
mg
tissue)

Not
Detectable
(
N.
D.)

Nectar,
meal,
oil
0.06
(<
LOQ)

Pollen
5.44
Flowers
4.88
Squares
8.19
Terminal
leaves
6.81
Young
leaves
Cry1F
Mean
Expression
(
ng
ICP/
mg
tissue)

Tissue
16
High
Dose/
Refuge
Assumptions

Single
or
major
resistance
gene

Recessive
inheritance

RRs
are
rare

Refuge
supplies
SS
(
unselected
source)


Random
mating
or
preferential
mating
 
RR
with
SS

High
dose
(
1998
and
2000
SAP)


25X
the
dose
required
to
kill
99%
of
the
susceptible
insects

>
95%
RS
will
be
killed
and
>
99.9%
of
the
susceptible
insects
will
be
killed
17
Methods
to
demonstrate
high
dose
1.
Serial
dilution
bioassay
with
artificial
diet
containing
lyophilized
tissues
of
Bt
plants
using
tissues
from
non­

Bt
plants
as
controls.
(
TBW
and
PBW)

2.
Bioassays
using
plant
lines
with
expression
levels
approximately
25­
fold
lower
than
the
commercial
cultivar.

3.
Survey
large
numbers
of
commercial
plants
in
the
field
to
see
if
Bt
plants
are
at
the
LD99.9
or
higher
to
assure
that
95%
of
the
heterozygotes
will
be
killed.
(
CBW
 
NC)
18
Methods
to
demonstrate
high
dose
(
cont.)

4.
Similar
to
#
3,
but
would
use
controlled
infestations
with
a
laboratory
strain
of
the
pest
that
had
an
LD50
value
similar
to
field
strains.
(
CBW
 
MS;
PBW;

TBW)

5.
Determine
if
a
later
instar
with
an
LD50
that
was
25X
higher
than
that
of
the
neonate
could
be
tested
on
Bt
plants
to
determine
if
95%
or
more
of
the
later
stage
larvae
were
killed.
(
TBW)
19
Dose
and
Functional
Dominance

TBW

High
dose
for
Cry1Ac
+

Cry1F(
>
99.9%)


High
dose
for
Cry1Ac
alone

Nearly
high
dose
for
Cry1F
alone

PBW

High
dose
for
Cry1Ac
(>
99.9%),
Cry1F
non­
toxic

Resistance
likely
to
be
functionally
recessive,
RS
likely
to
be
killed
on
WideStrike

CBW

Not
a
high
dose
for
Cry1Ac
+
Cry1F
(~
94%
mortality
 
MS
+

NC)


Not
a
high
dose
for
either
ICP
alone,
but
Cry1Ac
>
Cry1F

Resistance
less
likely
to
be
functionally
recessive

SAP
Question
#
1:
dose
and
functional
dominance
20
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
21
Biological
Factors

Adult
movement
and
dispersal

Larval
movement

Alternate
hosts

Population
dynamics

Metapopulation
dynamics
­
important
consideration
for
CBW
22
Adult
and
Larval
Movement
Mobile*

Extensive
(
Fitt,
1989)

CBW
Not
Mobile
Limited
(
Tabashnik
et
al.,
1999)

PBW
Mobile
Moderate
(
Fitt,
1989)

TBW
Larvae
Adult
Pest
*
In
absence
of
a
high
dose,
the
consequence
of
larval
movement
on
the
population
rate
of
adaptation
is
relatively
small,
since
heterozygote
survival
is
already
relatively
high
compared
to
SS
larvae.
23
Alternate
Hosts

HOSTS
database
for
Nearctic
region
(
host
plants
of
the
world's
Lepidoptera)


TBW:


66
species
from
20
families

wild
hosts
early
and
late

ability
of
alternate
hosts
to
support
complete
insect
development
during
the
summer
is
unclear

PBW:


26
species
from
5
families

most
closely
related
to
cotton

non­
cotton
hosts
not
important
to
adaptation
24
Alternate
Hosts

CBW:


108
species
from
30
families

Long­
distance
dispersal
then
host
plants
outside
the
immediate
cotton­
growing
area
act
as
important
sources
of
non­
selected
populations
[
Metapopulation
dynamics]


Gould
et
al.
(
2002)
­
carbon­
isotope
ratios
in
CBW
adults
collected
in
the
mid­
south
and
southwest
US,

indicate
the
more
insects
emerge
from
alternate
hosts
than
from
cotton
for
most
of
the
year
25
Alternate
Hosts

Host
data
base
 
extensive
alternate
hosts

CBW
Model

Includes
alternate
hosts
in
two
agroecosystems
(
NC
and
Delta)


Includes
multiple
ICPs
(
Cry1F,
Cry1Ac,
Cry2A)


Gould
et
al.
2002
carbon
isotope
analysis
showing
N­
S
movement
of
CBW
and
influence
of
alternate
hosts

SAP
Question
#
3:
scientific
adequacy
of
database
and
whether
additional
field
data
are
needed
26
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
27
Genetic
Factors:
Functional
Dominance

Functional
dominance
of
R­
allele
(
Is
the
R­
allele
genetically
completely
recessive)


TBW
and
PBW,
Dominance
=
<
0.05,

functionally
recessive
[
95%
heterozygotes
killed]


CBW,
Dominance
=
0.5,
additive
28
Genetic
Factors:
Initial
R
Frequency

Initial
R
frequency
is
rare

TBW:
0.0015,
recessive
(
Gould
et
al.
1997)


CBW:
0.00043,
incompletely
dominant
(
Burd
et
al.
2001)


PBW:
variable,
0
to
0.16
(
Tabashnik
et
al.

2000);
R­
allele
frequency
dropped
in
subsequent
years,
recessive;
fitness
costs
to
resistance
­
overwintering
and
survival
on
non­

Bt
cotton
plants
(
Carri

re
et
al.
2001b
and
c)
29
Genetic
Factors:
Cross­
Resistance

Cross­
resistance
among
Bt
ICPS

Potential
for
genes
that
confer
cross­
resistance
by
reduced
binding

Potential
to
occur
through
protein
digestion
in
the
midgut,
broad
cross­
resistance

SAP
Question
#
2:
cross­
resistance
potential
Cry1F
and
Cry1Ac

Cross­
resistance
between
Bt
and
other
control
mechanisms
(
e.
g.,
pyrethroids,
carbamates,
spinosad)


Not
expected
based
on
mode
of
action
30
Cross­
Resistance
Potential:
Cry1F
and
Cry1Ac

Resistance
to
Bt
proteins
may
occur
through
several
different
mechanisms.


Two
common
Bt
resistance
mechanisms
(
Ferré
and
Van
Rie,
2002;
Tabashnik,
1994):


Detoxification

Receptor
binding
modification
(
most
common)


Loss
of
function
(
i.
e.,
binding),
resistance
expected
to
be
recessive
(
Ferré
and
Van
Rie,
2002)


Cry1F
and
Cry1Ac
 
share
binding
sites
and
have
unique
binding
sites
in
TBW
and
CBW

Shared
binding
may
lead
to
cross­
resistance,
enhance
survival
against
both
Cry1Ac
and
Cry1F
31
Cry1Ac
and
Cry1F
Binding
Patterns
in
TBW
and
CBW

Protein­
pest
specificity
is
mediated
by
ICP­
binding
midgut
receptors

Cry1F
and
Cry1Ac:

shared
and
unique
binding
sites
260
176/

170
32
Cross­
Resistance
Potential
­
CBW

Radiolabeled
Cry1Ac
(
Dow:
Sheets
and
Storer,
2001):


60%
of
Cry1Ac
binding
is
to
Cry1F
receptors,
40%
of
Cry1Ac
binding
is
to
non­
Cry1F
receptors

Incomplete
shared
receptor
binding
=
incomplete
crossresistance
when
resistance
is
mediated
by
receptor
changes.


Thus,
a
mutation
in
a
gene
that
codes
for
a
receptor
that
binds
both
Cry1Ac
and
Cry1F
will
not
prevent
all
binding
to
either
ICP,
and
thus
alone,
will
not
allow
high
survival
of
the
insect
bearing
even
two
copies
of
it
on
WideStrike
cotton.


Radiolabeled
Cry1F
­
Problems
with
radiolabeling
affect
the
Cry1F
activity,
but
expect
incomplete
shared
receptor
binding
and
same
conclusions
as
above
33
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
34

Peck
et
al.
(
1999)
for
TBW

Dow
(
2003)
for
CBW

SAP
Questions
#
4
and
#
5
regarding
TBW
and
CBW
models
Models
35
Peck
et
al.
(
1999)
TBW
Model

Spatially
explicit,
stochastic
model

Examined
refuge
size
and
spatial
pattern
of
Bt
and
non­

Bt
plants
(
such
as
seed
mixes
and
external
refuge)
on
resistance
development,
and
the
effects
of
varying
the
spatial
pattern
each
year.


20%
refuge
delayed
resistance.


Greater
durability
if
refuge
remains
the
same
from
year
to
year,
but
localized
resistance
foci

If
structured
refuge
is
moved
each
year,
resistance
predicted
in
approximately
17
years.
36
Peck
et
al.
(
1999)
TBW
Model

Durability
for
WideStrike
greater
than
predicted
by
Peck
et
al.
(
1999)
­
>>
10X

Simulations
of
pyramided
ICPS
(
e.
g.
Roush
1997,

Gould
1998)
show
that
adding
an
additional
ICP
to
the
plant
always
delays
the
development
of
resistance
to
each
ICP
individually

Initial
R­
allele
frequency
of
0.03,
value
much
higher
than
the
frequency
of
Cry1Ac
R­
alleles
in
TBW
populations,
0.0015
(
Gould
et
al.
1997)
37

Adapted
Storer
et
al.
(
2003)
CBW
model
for
WideStrike

Spatially­
explicit,
stochastic

Alternate
hosts

North
Carolina
and
Mississippi
Delta
agroecosystems

Multiple
ICPs:
Cry1F,
Cry1Ac,
Cry2Ab

15­
year
time
horizon
Dow
CBW
Model
38

R­
allele
frequency
(
unmutated,
no
fitness
costs)
=
0.001

1
in
1,000,000
individuals
will
be
homozygous
for
the
mutated
form
of
one
of
the
receptors.


4
in
1,000,000
will
be
heterozygous
for
the
mutated
form
of
two
receptors.


R­
alleles
are
assumed
to
be
functionally
additive,
moderate
dose
(
i.
e.,
functional
dominance
=
0.5)

DAS
CBW
Model
cont 
39
Agroecosystems
in
Model
North
Carolina
Mississippi
Delta
50%
soybean,
25%
maize,
25%
cotton
62%
soybean,
8%
maize,
30%
cotton
Maize­
1st
two
generations;
cotton
­
2nd
two
generations
each
year;
weeds
 
1st
and
last
generations;
soybeans
 
2nd
and
3rd;
10
X
10
fields
modeled
(
Storer,

2002)
40
DAS
CBW
Model:
Simplified
Binding
Map

Simplified
possible
receptors
to
3
(
A,
B,

and
C)
from
6
or
more

There
are
two
loci
at
which
R­
alleles
can
lead
to
adaptation
to
WideStrike;
one
for
receptor
A
and
one
for
receptor
B.
Proportion
of
Cry1Ac
binding
to
Receptor
A
v.
B
­
binding
in
the
model
­
binding
not
included
in
the
model
(
Storer,
2002)
41
Impact
of
Shared
Binding
on
Population
Fitness
 
Sensitivity
Analysis

x
=
20­
60%:
Intermediate
level
crossresistance

Selection
at
both
loci
occurs
on
all
Bt
cotton
and
Bt
corn,
least
change
in
population
fitness.


Adaptation
to
Cry1Ac
and
Cry1F
occurs
most
slowly.


Selection
pressure
exerted
by
Cry1Ac>
Cry1F
because
Cry1Ac
in
Bollgard,
Bollgard
II,
and
WideStrike

Binding
data
indicate
that
intermediate
levels
are
appropriate:
60%
of
Cry1Ac
binds
to
Cry1F
receptor

x
=
0%:
No
cross­
resistance

x
=
100%:
Complete
cross­
resistance
0
0.2
0.4
0.6
0.8
0%
20%
40%
60%
80%
100%

Degree
of
Shared
Binding,
x
(
i.
e.
relative
amount
Cry1Ac
binds
to
Cry1F
receptor)

Population
fitness
on
Bt
cotton
MXB­
13
MXB­
13
initially
Bollgard
BG
initially
(
Storer,

2004)

NC
Agroecosystem
42
CBW
Mortality
for
Model

Cry1F
line
alone:
67%


Cry1Ac
line
alone:
97%


WideStrike
(
Cry1Ac
+
Cry1F):
97.2%,
Cry1Ac
shared
binding
=
60%


Bollgard
(
Cry1Ac
alone):
80%
(
Lambert
et
al.
1997)


Bollgard
II
(
Cry2Ab2
+
Cry1Ac):
96%
43
CBW
Fitness
Values
for
Model

To
understand
mortality
of
insects
carrying
one
or
more
Ralleles
to
understand
the
durability
of
WideStrike

Functional
dominance
of
resistance
on
each
Bt
cotton
type

Degree
of
shared
binding:

60%
of
Cry1Ac
binds
to
Receptor
A,
40%
to
Receptor
B

R­
alleles
are
assumed
to
be
functionally
additive,
functional
dominance
=
0.5,
due
to
lack
of
high
dose

Two
loci
at
which
R­
alleles
lead
to
adaptation
to
WideStrike
(
A
and
B)


Cry1Ac
fitness
depends
on
genotypes
for
Receptor
A
and
B.


Cry1F
fitness
depends
on
genotype
for
Receptor
A

Cry2
fitness
depends
on
genotype
for
Receptor
C

Calculate
fitness
values
for
the
model
(
27
possible
genotypes)


Values
indicate
the
survival
probability
of
each
genotype
on
each
Bt
cotton
type.
44
CBW
Adaptation
Assumptions

ICP
binding
to
the
individual
binding
receptors
included
in
the
model
is
all
functional
and
leads
to
the
insecticidal
activity.


Adaptation
to
the
ICPs
is
assumed
to
be
caused
by
mutations
to
the
midgut
receptors
and
that
each
receptor
requires
a
different
mutation

Complete
adaptation
to
both
ICPs:
insect
would
have
to
be
homozygous
for
two
receptor
mutations

Heterozygous
insects
(
functional
dominance
=

0.5)
have
a
fitness
halfway
between
that
of
SS
and
RR
insects
45
Market
Share
of
WideStrike
Vs.
Bollgard
or
Bollgard
II:
Impact
on
Population
Fitness
°
Complex
of
ICPs
reduces
the
selection
pressure
to
any
one
product.

°
WideStrike
had
minimal
impact
on
the
rate
at
which
CBW
may
adapt
in
the
Mississippi
Delta
and
North
Carolina
agroecosystems.

°
Marketshare
of
WideStrike
with
Bollgard
II
results
in
slower
adaptation
because
insects
are
faced
with
3
ICPs.

°
In
Delta,
population
fitness
decreases
due
to
influence
of
immigrants.

(
Storer,
2002)
46
Refuge
Size
Impact
on
Population
Fitness
°
Refuge
size,
whether
sprayed
or
unsprayed,
had
minimal
impact
on
CBW
population
fitness
on
WideStrike
after
15
years.

°
In
the
Delta,
the
immigrating
non­
selected
population
from
alternate
hosts
further
reduces
the
local
rate
of
adaptation.
The
local
structured
refuge
only
supplies
a
small
proportion
of
the
non­
selected
insects.
(
Storer,
2002
50%
WideStrike,
25%
Bollgard,
25%
Bollgard
II
47
Sensitivity
Analysis

Most
important:


Proportion
of
the
landscape
planted
to
soybean

Soybean
flowering
dates

Immigration
of
non­
selected
populations

Initial
R­
allele
frequency

Fitness
costs
of
R­
alleles.


Moderate
effects:


Functional
dominance
of
R­
alleles
on
each
crop

Dispersal
probability

Larval
development
duration.
48
WideStrike
CBW
Adaptation
Conclusions

WideStrike
durability:
Modeling
indicates
no
significant
change
in
population
fitness
in
CBW
over
15­
year
time
horizon

Moderate
dose
for
Cry1Ac
and
Cry1F
against
CBW

Incomplete
cross­
resistance
 
60%
shared
binding

Modeling
is
conservative;
fewer
binding
receptors

Alternate
hosts
add
to
durability;
although
more
field
data
needed

Durability
similar
to
Bollgard
II
(
Cry1Ac
+
Cry2Ab)
49
WideStrike
TBW
Adaptation
Conclusions

WideStrike
durability
greater
than
predicted
by
Peck
et
al.
(
1999)


Widestrike
stack
(
2
ICPs)
expresses
a
high
dose
against
TBW,
more
durable
than
high
dose
single
gene
product.


TBW
exhibits
similar
patterns
in
binding
studies
as
does
CBW,
i.
e.,
some
shared
and
some
unique
receptors.


Incomplete
cross­
resistance
50
WideStrike
PBW
Adaptation
Conclusions

WideStrike
expresses
a
high
dose
of
Cry1Ac,
like
Bollgard
(
Cry1Ac)
cotton.


Single
gene
product,
Cry1Ac,
for
PBW

Cry1F
is
not
effective
against
PBW.
51
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
52
WideStrike
IRM
Plan:
Refuge
Options

5%
external,
unsprayed
refuge:
Five
percent
of
the
cotton
fields
must
be
planted
to
non­
Bt
cotton
and
not
be
treated
with
any
lepidopteran­
control
technology.
The
refuge
must
be
at
least
150
ft.
wide
(
preferably
300
ft.)

and
within
½
mile
(
preferably
adjacent
or
within
1/
4
mile
or
closer)
of
the
Bt
cotton.


20%
external,
sprayed
refuge:
Twenty
percent
of
the
cotton
fields
must
be
planted
to
non­
Bt
cotton
and
may
be
treated
with
lepidopteran­
active
insecticides
(
or
other
control
technology)
except
for
microbial
Bt
formulations.

The
refuge
must
be
within
1
mile
(
preferably
within
½
mile
or
closer)
of
the
Bt
cotton
fields.
53
WideStrike
IRM
Plan:
Refuge
Options
Cont.


5%
embedded
refuge
for
TBW
and
CBW:
Five
percent
of
a
cotton
field
(
or
fields)
must
be
planted
with
non­
Bt
cotton
as
a
block
within
a
single
field,
at
least
150
ft.
wide
(
preferably
300
ft.
wide)
or
single
field
blocks
within
a
one
mile
squared
field
unit.
The
refuge
may
be
treated
with
lepidopteran­
active
insecticides
(
or
other
control
technology)
only
if
the
entire
field
or
field
unit
is
treated
at
the
same
time.


For
PBW:
One
single
row
of
a
non­
Bt
cotton
variety
must
be
planted
for
every
6
to
10
rows
of
Bt
cotton.
This
can
be
treated
with
lepidopteran­
active
insecticides
(
or
other
control
technology)
only
if
the
entire
field
is
treated
at
the
same
time.
54
WideStrike
IRM
Plan:
Refuge
Options
Cont.


Community
refuge:
Farmers
can
combine
neighboring
fields
within
a
one­
mile
squared
field
unit
that
act
as
a
20%
sprayable
refuge
or
the
5%

unsprayed
refuge.
Participants
in
the
community
refuge
option
must
have
a
community
refuge
coordinator
and
appropriate
documentation
is
required.
55
WideStrike
IRM
Plan
Cont.


Grower
agreements
and
annual
affirmation

Grower
education
program

Grower
compliance
program

Monitoring
for
insect
resistance

Remedial
action
plans

Additional
research
 
CBW
resistant
colonies
56
WideStrike
IRM
Plan
Conclusions

Conservative
plan
for
WideStrike:


Pyramided
toxins,
Cry1Ac
and
Cry1F,
for
TBW,

CBW

Incomplete
cross­
resistance

TBW
and
CBW
models
predict
high
durability
for
at
least
15
years

TBW:
high
dose
for
WideStrike;
high
dose
for
Cry1Ac
alone,
nearly
high
dose
for
Cry1F

CBW:
high
moderate
dose
for
WideStrike

PBW:
high
dose
Cry1Ac
57
WideStrike
IRM
Plan
Conclusions

Mix
of
Bt
toxins
(
Cry1Ac,
Cry1F
and
Cry2Ab)
in
market
place
will
reduce
selection
pressure
for
adaptation
­­­
especially
for
Cry1Ac
found
in
Bollgard,
Bollgard
II,
and
WideStrike

Any
plan
that
focuses
on
TBW,
CBW,
and
PBW
should
be
adequate,
to
maintain
susceptibility
in
secondary
pests,
such
as
armyworms
and
loopers

Consistency
with
existing
plans,
practical
and
implementable
58
Acknowledgements

Alan
Reynolds,
M.
S.,
OPP/
BPPD

Hilary
Hill,
M.
S.,
OPP/
BPPD

Tessa
Milofsky,
M.
S.,
OPP/
BPPD
59
Outline

Key
IRM
issues

What
is
WideStrike
cotton

Target
pests

Factors
in
pest
adaptation

Operational
factors

Biological
factors

Genetic
factors

Models

Resistance
management
plan

SAP
Questions
60
WideStrike
IRM
Questions
for
the
SAP
1.
Dose­
TBW,
CBW,
PBW.
The
Agency
asks
the
SAP
to
comment
on
the
Agency's
analysis
of
dose
for
TBW,

CBW,
and
PBW,
the
likelihood
that
resistance
will
be
inherited
as
a
recessive
trait,
and
its
impact
on
insect
resistance
management
for
WideStrike
cotton.
61
WideStrike
IRM
Questions
for
the
SAP
2.
Cross­
resistance.


The
Agency
asks
the
SAP
to
comment
on
EPA's
conclusion
that
incomplete
shared
binding
of
Cry1Ac
and
Cry1F
receptors,
in
TBW
and
CBW,
is
expected
to
lead
to
incomplete
cross­
resistance
and
thus
the
likelihood
of
enhanced
survival
on
WideStrike
cotton
is
expected
to
be
small.


Please
comment
on
EPA's
conclusion
that
resistance
is
more
likely
to
be
associated
with
receptor
binding
modifications
rather
than
other
mechanisms
of
resistance
such
as
detoxification
in
the
midgut
lumen
by
proteases
that
cleave
the
insecticidal
control
protein(
s),
metabolic
adaptations,
protease
inhibition,
gut
recovery,
and
behavioral
adaptations.
62
WideStrike
IRM
Questions
for
the
SAP
3.
CBW
Modeling.
The
Agency
asks
the
SAP
to
comment
on
the
predictions
made
by
the
DAS
CBW
model,
i.
e.,

the
likelihood
that
the
population
fitness
of
CBW
on
WideStrike
cotton
in
a
15­
year
time
horizon
will
remain
unchanged,
even
without
a
high
dose
for
either
Cry1Ac
or
Cry1F
and
incomplete
cross­
resistance
(
60%
of
Cry1Ac
binds
to
the
Cry1F
receptor).

4.
TBW
Modeling.
The
Agency
asks
the
SAP
to
comment
on
the
relative
WideStrike
cotton
durability
against
TBW
using
the
Peck
et
al.
(
1999)
model.
63
WideStrike
IRM
Questions
for
the
SAP
5.
Alternate
hosts.
The
Agency
asks
the
SAP
to
comment
on:


a)
the
sufficiency
of
the
WideStrike
cotton
database
to
address
the
issue
of
CBW
alternate
hosts
as
natural
refugia,
and,


b)
whether
additional
data
are
needed
on
the
larval
and
adult
production
of
CBW
on
each
alternate
host
for
each
generation
relative
to
cotton
and
WideStrike
cotton
and
the
spatial
scale
and
source
of
moth
production
to
confirm
the
effectiveness
of
CBW
alternate
hosts
as
natural
refugia.
64
WideStrike
IRM
Questions
for
the
SAP
6.
Refuge
requirements.
The
Agency
asks
the
SAP
to
comment
on
the
scientific
data
available
to
support
the
proposed
IRM
plan
and
whether
that
data
support
a
delay
in
resistance
of
TBW,
CBW,
and
PBW
resistance
to
the
Cry1F
and
Cry1Ac
proteins
expressed
in
WideStrike
cotton
for
at
least
15
years.
