## Comments to US EPA Scientific Advisory Panel

Agricultural Biotechnology Stewardship Technical Committee 

# Corn Rootworm Resistance Monitoring for Bt Corn Plant

Incorporated Protectants (PIPs)

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# Who is ABSTC?

 Ag

- Biotech Companies with US Bt crop registrations, or who are major trait providers

– Bayer Crop Science

– Dow AgroSciences

– Monsanto

– DuPont Pioneer

– Syngenta Seeds

 Develops research and educational programs that promote responsible use of Bt corn products

 Works with EPA and other key stakeholders to implement effective IRM programs

 Committed to applying the best science available to issues that enable farmers, consumers, and the environment to benefit from the products of agricultural biotechnology

# 1) Annual Corn Rootworm Sampling to Assess Bt Susceptibility

 

### ABSTC member companies collectively sample corn rootworm populations to monitor for resistance

 

### Annual population sampling and screening is unlikely to find populations with emerging resistance

– Rootworm resistance to Bt corn traits is highly localized

– Field

- specific cropping history

 Continuous corn

 Continuous use of single mode of action

– Field

- specific management practices

– Generally limited corn rootworm adult dispersal out of corn fields


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# 1) Annual Corn Rootworm Sampling to Assess Bt Susceptibility

 

## Identification of resistant individuals is not realistic

– 

### Lack of high dose allows susceptible insects to survive in field

– 

### Survivors in any Bt corn field are on average likely to be less sensitive to the Bt protein than those that died

– 

### Resistance may involve complex genetics and mechanisms

– 

### Molecular markers for resistance alleles are not available



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# 1) Annual Corn Rootworm Sampling to Assess Bt Susceptibility

 

## Sentinel plots of non

- Bt corn can provide reference collections representing four region

- wide corn rootworm biotypes for comparing with populations of interest collected in Bt corn fields showing unexpected root damage
 

## ABSTC recommends that annual sampling and screening program be discontinued
 

## ABSTC recommends establishment of sentinel plot program to provide region

- wide reference collections

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# 2) Corn Rootworm Sampling in Response to Damaged Bt Fields

 

## ABSTC member companies individually investigate reports of unexpected damage to their Bt corn products

 

## Investigations are designed to

– 

### Confirm root injury is unexpected

– 

### Confirm corn rootworm was responsible for the damage

– 

### Confirm that the damaged corn was expressing the Bt protein

– 

### Collect rootworm adults for future bioassays, if available



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# 2.i) Unexpected Damage Thresholds

 

### Bt corn products for corn rootworm protection differ in their protection of corn roots

 

### Bt corn root injury is related to overall pest population pressure and does not always indicate presence of resistance

 

### Even so, ABSTC recommends the following rules of thumb for unexpected damage thresholds for existing products

 Single MOA Products: NIS ≥ 1.0 on more than 50% of corn roots assessed
 Dual MOA Products: NIS ≥ 0.75 on more than 50% of corn roots assessed


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# 2.ii) Root sampling goals

1. 

## Characterize damage in the affected areas of a field

2. 

## Define the extent of unexpected damage across the field

 

## ABSTC recommends appropriate sampling that addresses the goals above

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# 2.iii) Adult corn rootworm sampling

 

## Corn rootworms move within a field to forage for fresh silks and pollen

 

## ABSTC recommends rootworm adult samples be collected from wherever most adults are found in the field

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# 2.iv) Sentinel plots to assess resistance allele frequency in the area

 

## It is not realistic to attempt to measure resistance allele frequencies, especially not with sufficient resolution to measure gradients

 

## Sentinel plots would be difficult to implement within a rootworm resistance management program  

## ABSTC recommends registrant revisits farms with unexpected damage the following season to assess rootworm management actions and collect rootworm adults if available.

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# 3) Diagnostic Assays

 

### ABSTC member companies individually conduct assays to monitor for resistance to their products

 

### It is not possible to measure resistance allele frequencies accurately or precisely

 

### Mean population fitness, such as LC50 or survival and development rates under field

- relevant exposure conditions, are most relevant for non

- high

- dose products

 

### On

- plant and diet bioassays both have value in understanding rootworm response to Bt proteins
 

### ABSTC is working towards a standardized diet for bioassays across proteins as a desired goal



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# 4) Defining resistance

 

### Resistance is quantitative and there is not a biologically meaningful threshold of sensitivity that represents resistance

 

### Because current corn rootworm

- protected Bt corn events are not “high dose” small changes in population response can be biologically meaningful but may not have pest

- management implications
 

### ABSTC recommends a focus on triggers for additional rootworm management actions rather than on definitions of resistance



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# 5) Determining Remedial Action Areas

 

### ABSTC member companies do not share customer

- specific data

 

### Measuring resistance allele frequency gradients is likely to be intractable

 

### Corn rootworm resistance is relevant if changes in rootworm management are warranted
 

### ABSTC recommends that remedial action zones be established based on patterns of field performance
 

### ABSTC recommends focusing on fields that have a similar crop and trait history to those where resistance is known to have developed



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# 6) Containment/mitigation of resistance

 

### Goals of remedial action programs include

– Reduce economic impact of resistance in affected fields and farms

– Reduce rate of spread of resistance

 

### Population elimination is unrealistic

 

### Remediation measures should focus on sound Integrated Pest Management principles
 

### ABSTC has developed harmonized “Best Management Practices” for corn rootworm that are intended to be effective at delaying and reducing the impact of resistance



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# CRW Best Management Practices Guidelines (2013)

• Lead recommendation: Regardless of crop or trait history, CRW pressure, or CRW resistance, rotation to a non

- CRW host crop (e.g. soybeans) is the preferred recommendation

1. Break the CRW cycle

1. Rotate to non

- host crop
2. Trait rotation (continuous corn)

– Rotate different dual (pyramided) or single MOA Bt trait products that provide effective below

- ground protection against CRW

• Do not plant more than 3 consecutive years to the same single Bt

- traited corn product 2. Manage the insect population

1. Scout and assess potential CRW pressure levels
2. Manage high CRW populations

• More frequent crop rotation in areas with high CRW pressure (suggest no more than 3 years of continuous corn planting)

• Use dual MOA CRW

- traited products

• Adult beetle sprays 3. Protect corn plants from root injury

1. Prescribed use of soil

- applied insecticides/high rate seed treatments to manage larval injury Note: All guidelines refer to management of individual fields. MOA = mode

- of

- action 

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# CRW management decision tree based on following defined criteria:

 

## CRW pressure

– 

### CRW pressure expected based on cropping history and previous adult population monitoring or management

 

## CRW trait resistance concern

– 

### Traited

- field categorized as “Unexpected Damage” (UXD)

– 

### Field history along with observed lodged corn and root damage ratings suggesting UXD 

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## Lead CRW Management Recommendation: Crop Rotation*

CRW Pressure LOW

Corn Rootworm Trait Resistance Concern? Scout fields to determine CRW pressure**

CRW Pressure HIGH Crop Rotation? Yes Non

- host crop N
o

• CRW traits

− Dual MOA

− Single MOA

• Soil insecticide

• Seed treatment N
o Y
e
s

• Dual MOA CRW trait + soil insecticide

• Different single MOA CRW

trait + soil insecticide

• Non

- Bt + soil insecticide • Dual MOA CRW trait

• Single MOA CRW trait (avoid planting same single trait MOA > 3 yrs)

• Non

- Bt + soil insecticide

*Use appropriate rotational practices in your region. Manage the CRW rotational variant appropriately. **Scouting CRW adults in July & August can help manage CRW adult populations and/or predict CRW pressure for the following year, which can assist in determining management options. Other indicators of pressure include observed root damage and or lodged corn during the season or at harvest.

# Summary

 Corn rootworm management has presented huge challenges for 60+ years

 Bt corn continues to be the most reliable and effective rootworm management tool

 Proactive resistance management is critical to extending the durability of Bt corn

– Plant required refuges (use products with integrated refuge seed)

– Avoid multiple years of continuous corn with the same single mode of action trait

 When resistance begins to reduce the performance of Bt corn, rootworm populations can continue to be managed with a combination of traits and other management practices

 Crop rotation is generally a highly effective pest management and resistance management tactic

 Remediation measures should be commensurate with the level and extent of resistance and should be flexible to recognize the practical realities of agriculture


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