Insect Resistance Management for Bt Crops Bt??????????

1
Insect Resistance Management for Bt
CropsBt??????????

• Tessa Milofsky, M.S. and Sharlene Matten, Ph.D.
• ??. ????? ??
• ???.?? ??
• U.S. Environmental Protection Agency
• Office of Pesticide Programs
• ????? ????????

2
IRM what is it??????????
Insect resistance management (IRM) is a strategy
to mitigate the development of insects resistant
to a pesticide (e.g., resistance to Bacillus
thuringiensis or Bt) ???????(IRM)???????????(??
?BT)????????????.
3
IRM why is it important?IRM????

• Maintaining the efficacy of Bt, a low-risk
  pesticide, is beneficial for the following
  reasons
• ????????Bt?????????
• Bt replaces higher risk pesticides
• Bt?????????????????
• Less exposure of nontarget organisms to
  superficially applied pesticides
• ?????????????????
• Use of Bt crops may provide greater profits to
  farmers, due to reduced use of insecticides
• ???????????,Bt??????????????

4
Critical components of IRM planIRM?????????

• Pest biology ?????
• Dose ??
• Cross-resistance ????
• Refuge ???
• Modeling ????
• Resistance monitoring ????
• Remedial action ????
• Compliance assurance ?????
• Grower education ?????

5
Pest biology?????

• Important factors include
• Number of insect generations per year
• Host range
• Insect movement and dispersal patterns
• Mating and ovipositional behavior
• Population dynamics
• ????
• ?????????
• ?????
• ??????????
• ???????
• ????

6
Pest biology an example???????

• European corn borer (ECB), Ostrinia nubilalis
• 1-4 generations per year
• Polyphagous (prefers corn)
• Movement
• Larvae - can move from plant-to-plant within a
  field
• Adults - mostly local movement, but some long
  distance migratory movement can occur
• ?????(ECB)
• ????1-4?
• ???(????)
• ??
• ?????????????????
• ??????????,????????????

Male ??
Female ??
ECB
late instars ????
7
Dose ??

• Dose the amount of toxin expressed over time by
  a transgenic crop, relative to the susceptibility
  of a target pest can be determined through field
  efficacy trials or laboratory bioassays
• ????????????????????, ???????????
  ????????????????????.
• High dose at least 25x the amount of toxin
  needed to kill all susceptible target insects
  preferred over low dose events for refuge-based
  IRM strategies
• ???????????????????25? ??????????????????,??????
  ???????????????

8
Dose assumptions????
100

• Three genotypes for resistance/susceptibility
  (SS, rS, rr)
• Resistance (rr) is recessive and rare
• Refuge supplies SS (homozygous susceptible)
  genotype
• Random mating
• rr x SS ? rS
• rS x SS ? rS or SS
• SS and rS susceptible to high dose
• ????/??????(SS,rS,rr)
• ????(rr)????,???
• ?????SS(????)
• ????
• rr x SS ? rS
• rS x SS ? rS or SS
• SS?rS??????

LC50
0
?
?
9
Dose levels some examples???????????

• Lepidopteran-active corn (Cry1Ab Cry1F)
• High dose
• European corn borer (ECB), Ostrinia nubilalis
• Southwestern corn borer (SWCB) Diatraea
  crambidoides
• Non-high dose
• Corn earworm (CEW), Helicoverpa zea
• ??????? (Cry1Ab Cry1F)
• ???
• ????? (ECB), Ostrinia nubilalis
• ????? (SWCB) Diatraea crambidoides
• ????
• ????? (CEW), Helicoverpa zea

ECB
female
male
late instars
WCR
10
Dose levels some examples???????????

• Rootworm-active corn (Cry3Bb1, Cry34/35, mCry3A)
• Non-high dose
• Western corn rootworm (WCR), Diabrotica virgifera
  virgifera
• Northern corn rootworm (NCR), D. barberi
• Mexican corn rootworm (MCR), D. virgifera zea
• Secondary pests
• Non-high dose for some pests
• ?????? (Cry3Bb1, Cry34/35, mCry3A)
• ????
• ?????? (WCR), Diabrotica virgifera virgifera
• ?????? (NCR), D. barberi
• ??????? (MCR), D. virgifera zea
• ????
• ????

ECB
female
male
late instars
WCR
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Cross-resistance????

• When resistance to a single Bt toxin confers pest
  resistance to a cluster of related toxins
• Factors affecting cross-resistance include
• Similarity/dissimilarity of commercialized toxins
• Use of single toxin versus multiple toxins
• Level of resistance in an insect population
• ?????Bt????????????????????????
• ???????????
• ?????????
• ????????????
• ?????????

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Cross-resistance an example(????????)

• Binding site diagram for European corn
  borer(???????????)

(??)
European corn borer (based on Hua, G., Masson,
L., Jurat-Fuentes, J. L., Schwab, G., Adang, M.
J. 2001. Binding analyses of Bacillus
thuringiensis Cry d-endotoxins using brush border
membrane vesicles of Ostrinia nubilalis. Appl.
Env. Microbiol. 67 872-879)
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Refuge ???

• Any host plant that does not produce Bt toxin and
  has not been treated with conventional Bt
  formulations (may be treated with non-Bt
  insecticide)
• ?????Bt?????????Bt???????????(????Bt??????)
• Enables mating between resistant and susceptible
  adults, resulting in production of susceptible
  offspring
• ??????????????????????

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Refuge options ??????

• Structured refuge specified size, location in
  relation to Bt field, and crop/plant composition
• Community-based refuge neighboring growers
  establish shared structured refuge
• Unstructured or natural refuge use of
  alternative host plants/crops in place of defined
  refuge
• ?????????,?????Bt?????????????,????????,????
• ?????????????????????????????
• ??????????????????????????????????????????

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Refuge options ??????

• Seed bag mix Bt seed bags contain Bt seed and
  non-Bt seed (e.g., 80 Bt, 20 non-Bt) seed may
  be bagged separately or mixed together
• Regional limit national/regional government
  enforced limit on Bt seed sales (e.g., 80 in
  defined region)
• ????????Bt?????????Bt??,????Bt??(??80Bt??,
  20?Bt??), ??????????????,?????????.
• ????????????Bt???????????(?? ??????,???80?Bt???
  ??)

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Structured refuge options????????
Block
In-field strips ????????
External block ??????
Seed mix
????
Internal block(s) ??????
Border (block) ??????
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Other refuge options???????
Bt cotton Bt?? w/ TBW
Soybean ??
Tobacco ??
Natural refuge ?????
Community refuge ???????
Tobacco budworm, ???? Heliothis virescens
80 Bt seed corn ????
20 non-Bt seed corn ????
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Bt corn refuge specifications an
exampleBt?????????

• 20 refuge required in corn belt 50 refuge
  required in corn/cotton region
• Structured refuge is required. Refuges may be
  planted in one of the following designs
• In-field strips (4-6 rows)
• Blocks (internal or external)
• Refuge requirements are the same for lepidopteran
  and coleopteran active products
• ?Bt????20????,???/??????50
• ??????????.??????????????
• ?????(4-6?)
• ???????

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Modeling ??

• Useful tool for predicting the likelihood of
  resistance, for evaluating the durability of IRM
  strategies, and for helping to focus data needs.
  Model components include
• Biological information (pest biology, population
  dynamics)
• Genetics (R-allele dominance/frequency, cross
  resistance)
• Operational aspects (dose, single/stacked
  toxin(s), refuge)
• ????????????,??IRM?????????????????????.
  ??????????
• ????(?????,????)
• ???(R-??????/??, ????)
• ????(??,???/?????,???)

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Resistance monitoring????

• Can help to prolong the efficacy of an insect
  resistant crop
• Designed to detect resistance 2-3 years before
  field failure
• Target pest sampling consists of
• Grower reports of unexpected pest damage in
  insect-protected crop fields
• Random population sampling
• Sampling based on pest prevalence in region
• Sampling target number of insects needed to
  determine resistance at plt0.01
• ???????????
• ??????????2-3?
• ????????
• ???????????????????????
• ??????
• ????????
• ?????????????????(plt0.01)

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Resistance monitoring (cont.)????(?)

• Bioassays are used to detect potential resistance
  in sampled populations. Assays include
• Pest susceptibility (LC50)
• Discriminating Dose (LC99)
• F2 screen
• Confirmation studies are used to verify
  resistance. Questions include
• Is there field failure?
• Is the insect resistance trait expressed?
• Is insect resistance trait inherited?
• ??????????????????. ??????
• ???????(LC50)
• ????(LC99)
• F2??
• ??????????.??
• ???????
• ?????????
• ????????

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Resistance monitoring positive hits for Bt corn
in the US? ???? ??Bt??????

• In 2001, mortality for one European corn borer
  (ECB) population (Kandiyohi, MN) was lt 99 in
  Cry1Ab discriminating dose assay
• Follow-up tests with Bt plant material revealed
  that population was not field resistant
• No field resistance confirmed for any monitored
  Bt corn pest
• 2001??Cry1Ab???????, ?????????????99
• Bt???????????????????
• ????Bt????????????????

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Remedial action plan????

• If resistance is confirmed through resistance
  monitoring, a remedial action plan is
  implemented to contain or slow the spread of
  resistant pest populations
• ????????????, ??????????????????

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Remedial action plan an example??????

• EPAs plan includes
• Mandatory reporting of suspected resistance
• Use of alternate control measures in affected
  areas
• Increased resistance monitoring
• Suspension of Bt crop sales in affected areas
• Investigation of cause of resistance
• ?????????
• ????????????????
• ??????????????
• ??????
• ????????Bt????
• ??????????

25
Compliance assurance?????

• Compliance measures implemented to ensure that
  growers comply with approved IRM program
• ????????????????????????????.

26
Compliance assurance an example???????

• EPA requires registrants to implement the
  following measures
• Contracts affirming grower agreement to comply
  with approved IRM strategy
• 3rd party grower surveys of IRM implementation
• On-farm field visits to verify IRM implementation
• Tips and complaints on non-compliers
• Suspension of seed access for non-compliers
• ??????????????????
• ???????????IRM??
• ????IRM????????
• ???????IRM?????
• ??????????????
• ????????????????

27
Grower education?????

• Education about the need for IRM, how to
  implement requirements, and grower responsibility
  in complying with IRM requirements
• ?IRM??????, ??????, ???????IRM????????????

28
Summary of EPAs IRM requirements for
lepidopteran-active Bt corn??????????????Bt??IRM?
???

• 20 refuge in corn belt 50 refuge in cotton
  belt
• Structured refuge required. Refuges planted in
  one of the following designs
• in-field strips (4-6 rows)
• blocks (internal or external)
• Industry-wide collaboration on compliance surveys
• ???????20???? ????????50
• ??????????.???????????????
• ????(4-6 ?)
• ??(?????)
• ???????????

29
Summary of EPAs IRM requirements for
lepidopteran-active Bt corn (cont.)?????????Bt??I
RM????(?)

• Industry-wide uniformity of
• Grower agreements
• Grower training
• Implementation of tips and complaints
• ???????????
• ?????
• ?????
• ????????

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Summary of EPAs IRM requirements for
lepidopteran-active Bt corn (cont.) ?????????Bt??I
RM????(?)

• Annual reporting requirements
• - Compliance assurance (e.g., surveys, grower
  contracts)
• - Changes to grower education
• - Resistance monitoring data
• - Sales data
• ??????
• ???????(????,?????)
• ????????
• ??????
• ????

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Data sources for EPAs IRM program?????IRM???????

• Published scientific literature
• Industry submissions
• Experts (academia, government, industry)
• Meetings (advisory panels, workshops, ESA, NC205,
  NC46)
• Field visits
• ????????
• ???????
• ??(???,??,???)
• ??(???,???,ESA,NC205,NC46)
• ????

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Keys to success at EPA?????(EPA)???????

• EPA is responsive to new scientific information
• EPA seeks scientific input from state and federal
  agencies, academic experts, and public interest
  groups
• EPA ????????????
• EPA ???????????,????????????????

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Keys to success at EPA?????(EPA)???????

• Conditional (time-limited) registrations enable
  EPA to adapt IRM requirements over time
• EPA negotiates regulatory changes with
  registrants and grower organizations
• ???????????EPA??IRM?????????????
• EPA ??????,??????????????

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IRM challengesIRM?????

• Plans are specific to the
• Pest/crop
• Country/region
• Bt selection intensity will be affected by
• Adoption/distribution of a Bt crop
• Cross-resistance potential with similar products
  (similar modes of action)
• ??????
• ??/??
• ??/??
• Bt?????????????
• Bt?????/??
• ????(??????)???????

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IRM challenges (cont.)IRM?????(?)

• Plans must be economically feasible to
• Growers (planting refuge)
• Industry (education, compliance, monitoring and
  evaluation)
• Government agencies (program evaluation, policy
  negotiation/implementation)
• ????(?????),????(??,???,?????)??????(????,????/??)
  ??,????????????.

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IRM challenges (cont.) IRM?????(?)

• Plans must be flexible/adaptable enough to
  consider
• Evolving science/new data
• New products
• Need for consistency across products
• ???????,????????,????
• ????/???
• ?????
• ????????

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Conclusions??

• IRM is based on strong science
• Plans must be
• Pest specific
• Flexible and adaptable
• Easy to implement
• Economical
• IRM?????????
• ????
• ???????
• ???,????
• ????
• ????