2

documenting its changes to the CRW resistance management program for Bt corn Plant 

Incorporated Protectants (PIPs).

EPA’s new framework for Corn Rootworm Resistance Management and Bt Corn (hereafter 

referred to as ‘framework’) is consistent with the recommendations received from the SAP and

expert corn rootworm entomologists, and addresses comments received from the public. The 

final, implemented framework includes new obligations of registrants that distinguish it from the 

previous resistance management program [5]

:

• Proactive Integrated Pest Management (IPM): Each Bt technology provider must develop 

and implement an educational outreach program that will help the company’s customers 

develop and implement a multi-year CRW management plan when using Bt corn, 

consistent with good IPM practices. The use of IPM is important as a means to reduce 

the likelihood of resistance, particularly with an insect like CRW that readily adapts to 

control efforts. IPM techniques for CRW encouraged in the educational outreach 

program include the rotation of fields to non-Bt corn crops (e.g., soybean) every few 

years, which should greatly reduce resistant corn rootworm populations.

• Responses to Cases of Unexpected Damage (UXD) to Bt Corn Fields: CRW damage to 

Bt corn fields may be an early indicator of developing resistance. A proactive and 

effective response to such cases may lessen (or eliminate) the impact of resistance in the 

CRW population if the damage is in fact due to resistance. As part of the new framework, 

Bt corn companies are required to investigate reports of damage and conduct tests to 

determine whether CRW are resistant to Bt corn. Companies must also implement “Best 

Management Practices” (BMPs), which are IPM-based strategies designed to reduce 

CRW populations in the affected field(s) and notify affected companies, neighboring 

customers, extension specialists, and crop consultants in areas where populations are 

found to be resistant.

• Enhanced Mitigation Strategies for Cases of Confirmed Resistance: When testing of 

CRW from UXD fields confirms resistance to Bt corn, companies are required to 

implement a response strategy to limit (or eliminate) the resistant population. Companies 

are required to take the following actions: notify affected parties (customers, extension 

specialists, and crop consultants) in areas with resistant populations; impose restrictions 

on the use of the Bt corn product with resistance in the affected area; and encourage 

growers to implement steps to reduce or eliminate the resistant population, such as crop 

rotation to soybean. 

• Additional information on the new CRW resistance management framework can be 

found on EPA’s web page at http://www.epa.gov/regulation-biotechnology-under-tscaand-fifra/framework-delay-corn-rootworm-resistance. See also the specific terms and 

conditions of registration specific to corn rootworm being imposed on these products. 

In developing the framework, EPA considered all comments received by growers, grower and 

agricultural groups, stakeholders, CRW experts, non-governmental organizations, and other 

government entities in refining the original proposal. EPA believes the new framework addresses 

concerns raised by a number of commenters that the changes to the CRW resistance management 

program as initially proposed in 2015 could be too prescriptive and not responsive to the needs 
3

of growers. The final framework allows flexibility for growers, while incorporating sound 

scientific standards to improve the old resistance management paradigm for CRW and Bt corn.

The intention of EPA’s framework is to extend the viability of Bt corn and future new CRW PIP 

products that reduce exposure to conventional pesticides in the environment and to humans. 

Though resistance to some currently available CRW Bt toxins has been documented, EPA

maintains that the framework should function well in areas inside and outside of the Corn Belt 

where resistance to these PIPs is not as prevalent. In areas with CRW resistance to Bt traits, the 

framework encourages growers to utilize sound IPM tools (e.g., rotating to a non-corn rootworm 

host) to manage corn rootworm populations. The framework also provides a strong incentive for 

registrants to encourage rotation to non-host crops such as soybean, which is the preferred and 

most effective method for managing resistance development in a field [6] [7]

. Most importantly, 

the framework implements a program for future technologies and ensures that these management 

tools are in place to delay resistance in corn rootworm at the onset of a new commercial PIP 

registration.

While the framework is legally binding for the biotechnology companies selling the Bt seed, it 

permits flexibility for growers and helps to encourage an adaptive multi-year corn rootworm 

management plan that will fit individual grower’s needs. Therefore, the burden on growers as a 

result of the new framework should be minimal. In addition, the framework seeks to preserve the 

benefits of Bt corn to growers for as long as possible.

B. Background on Corn Rootworm Resistance to Bt Corn

Academic researchers at the University of Iowa first documented in-field resistance to Cry3Bb1, 

one of the Bt PIPs used to control CRW, in 2009 [1] [8] [9], six years after the first commercial 

release of Cry3Bb1. The researchers used a novel on-plant bioassay rather than the established 

diet bioassay approach to identify resistance in the populations collected from the unexpected 

damage (UXD) fields. Subsequently, in 2012, resistance to Cry3Bb1 was also confirmed in parts 

of Illinois and Nebraska using the same assay approach [10] [11]. Academic reports of crossresistance between Cry3Bb1 resistant CRW populations and mCry3A were first published in 

2014; these reports further heightened EPA’s concerns. During this time, unexpected damage 

cases to mCry3A cornfields were also investigated and mCry3A resistance was confirmed [12]. In 

addition, EPA received a letter signed by 22 corn rootworm entomologists on March 7, 2012,

containing recommendations to the Agency on how best to prolong the lifetime of the Bt CRW

technology to which CRW were rapidly developing resistance [13].

Despite these field and academic reports, resistance to Bt toxins could not be confirmed using 

standard diet bioassay methodologies used by registrants, required by EPA for resistance 

monitoring, and described in the terms and conditions of registration for these PIP products. The 

reasons are as follows: 

• CRW are less sensitive to Bt than other insects and large amounts of toxin (or 

extrapolations from lower concentrations) are needed to obtain a 50% mortality (LC50 –
4

lethal concentration where 50% of the population dies) in the assays. Large amounts of 

toxin are prohibitively expensive to produce. 

• EC50 (effective concentration where 50% of the population is impacted) measures (more 

sensitive measure than LC50 used in diet bioassays) are still too variable and not sensitive 

enough to make a definitive resistance conclusions;

• Historical comparisons between populations collected in different years using EC50 data 

can also be limited if the testing methodology is modified or toxin lots are changed or 

sourced differently; 

• No diagnostic concentrations are available to identify potentially resistant populations 

from susceptible ones; and

• Differences in company used diets also affect the accuracy of diet bioassays and add 

further variability and uncertainty to the analysis of the data.

The resistance reports by academic research scientists in conjunction with the recommendations 

of public corn rootworm experts led the Agency to re-evaluate the current CRW resistance 

management program, including the use of diet bioassays. On September 27, 2013, the Agency 

released its white paper on corn rootworm resistance monitoring for Bt Plant-Incorporated 

Protectants (PIPs) [2] listing a series of “scientific uncertainties associated with corn rootworm 

resistance monitoring for Bt corn Plant-Incorporated Protectants (PIPs)” in preparation for a 

Scientific Advisory Panel meeting in December 2013 and proposed improvements for the CRW 

IRM program.

C. Scientific Advisory Panel Meeting and Recommendations to the US EPA

The US EPA’s Office of Pesticide Programs (OPP) convened a Scientific Advisory Panel

meeting on December 4-5, 2013, in Arlington, Virginia, to discuss the scientific uncertainties 

and the Agency’s proposal to improve six major components of the corn rootworm resistance 

management program. The Agency’s charge posed to the SAP asked for guidance on the 

following identified topics: 

1) Annual sampling to assess Bt susceptibility; 

2) Sampling in response to damaged Bt fields; 

3) Diagnostic assays; 

4) Defining resistance; 

5) Determining remedial action areas; and 

6) Containment and mitigation of resistance.

Public commenters, consisting of growers, ABSTC (Agricultural Biotechnology Stewardship 

Technical Committee, a consortium of the Bt corn companies ), and Non-Government 

Organization (NGO) representatives made presentations to the Panel on issues related to Best 
5

Management Practices (BMP), on-plant assay methodology resistance purposes, and rootworm 

resistance monitoring and development of resistance. 

EPA/OPP presented the SAP with an overview of CRW Insect Resistance Management (IRM)

and current resistance issues, including the scientific uncertainties associated with the established

resistance management program for CRW and Bt corn. EPA’s charge questions and the SAP’s 

response and recommendations are summarized below. The full report can be accessed on EPA’s 

website (http://www.epa.gov/sap/meeting-materials-december-4-6-2013-scientific-advisorypanel) and materials related to the SAP (e.g., public comments, Agency supporting materials, 

etc.) can be accessed on regulations.gov (Docket: EPA-HQ-OPP-2013-0490).

1) Replacing annual sampling with focused sampling: The Panel agreed with EPA that focused 

population sampling of unexpected Bt damage fields was more likely to detect resistant corn 

rootworm than random corn rootworm sampling in the Corn Belt.

2) Damage thresholds and sampling methodology in Bt fields with unexpected CRW damage 

(UXD): The Panel recommended that non-random transect sampling through the damaged area 

should be used to obtain root samples to assess the extent of the damage. The Panel agreed with 

EPA’s current practice of using Node Injury Scale (NIS) [14] scores as a threshold for unexpected 

damage in single trait Bt corn (>1.0 NIS) and pyramided Bt corn (>0.5 NIS). UXD fields that 

exceed these triggers are investigated for potential resistance. The panel recommended that root 

injury ratings be obtained with a non-random transect sampling approach.

3) Replacing diet assay with on-plant assays: Though EPA has proposed switching to on-plant 

assays for resistance determinations, the Panel stated that there were benefits to keeping the diet 

bioassays to monitor for resistance. However, the panel indicated that these standard assays did 

not serve as a proactive resistance detection tool. The Panel recommended complementing the 

on-plant assays with diet bioassays. 

4) Defining resistance: The Panel noted that several different measurements from on-plant assays 

may be needed to understand when a population is resistant. The Panel recommended the use of

a resistant laboratory colony alongside the suspected field population as a point of comparison. 

The Panel noted that resistance allele frequencies (perhaps the most direct way to assess 

resistance) cannot be used to make resistance conclusions because the technology has not been 

developed yet for CRW. 

5) Defining a mitigation action area in case of confirmed resistance: If CRW populations are 

determined to be resistant, the Panel cited to the following methods as potential approaches to 

demarcate a mitigation action area: adapt from corn rootworm population genetic/hybridization 

research conducted in Italy; model corn rootworm dispersal based on mark-recapture study or 

colonization from Europe; use spatial-temporal trends in bioassay data, information from the 

spread of the rotation resistant variant in the US Corn Belt, and shifts in abundance of adults as a 

measure of the resistance problem; or develop risk maps for fields and areas based on expert 

advice.

6) Mitigation of resistance: The Panel agreed with EPA that the use of theoretical models was a 

proactive and powerful method to test mitigation approaches and manage resistance. The Panel 
6

recommended that mitigation tools (e.g. crop rotation, planting of pyramids, non-Bt corn with 

SAI) should be used in a mosaic in the landscape and rotated on each field during each 

successive corn growing season, and noted that the sudden appearance of resistance in multiple 

locations should be an indication that resistance was high in CRW populations.

Other recommendations by the SAP:

IPM should be used with Bt deployment and not as a mitigation approach after field failure had 

occurred; chemical pesticides should not be used in conjunction with planting Bt corn for the 

purpose of corn rootworm control and is not consistent with IPM; in cases of resistance, a 

compromised Bt trait should not be used together with insecticide applications (this will mask 

resistance in the population and contribute to spreading resistance); the use of chemical 

insecticides to control adult corn rootworm (adulticides) should be a last resort.

D. EPA’s Proposal for an Improved Corn Rootworm Resistance Management 

Program

After having received the expert recommendations from the SAP, EPA developed a proposal [4]

to improve the current CRW resistance management program (proposal dated August 27, 2014)

consistent with those recommendations. Specifically, EPA identified the following elements as 

part of the proposal: 

• Integrated Pest Management stewardship program for Bt corn targeting CRW; 

• A standardized and robust response to unexpected damage in Bt corn; 

• Annual random monitoring requirement to be replaced by focused adult collections in 

unexpected damage sites; 

• Replacement of diet bioassay with more sensitive on-plant assays that are more 

reflective of conditions in the field; and 

• A defined, specific remedial action plan to be implemented in cases where of CRW

resistance has been confirmed.

EPA outlined its proposal to ABSTC in fall 2014. To ensure transparency, on January 28, 2015, 

EPA opened a public docket and initiated a 45 day public comment period on the 2014 proposed 

framework for CRW and Bt corn. During the initial comment period, several public requests

were received by the Agency to extend the comment period. In response, EPA added an

additional 30 days to the comment period which closed on April 15, 2015. 

Over the course of the public comment period, EPA received several requests from the public to 

provide additional explanations on the proposed framework. In the interest of transparency, the 

agency held multiple discussions with stakeholders. For example, on February 25, 2015, EPA

provided a webinar overview of the corn rootworm proposal to the Pesticide Program Dialogue 

Committee (PPDC) (accessible at https://www.epa.gov/pesticide-advisory-committees-andregulatory-partners/pesticide-program-dialogue-committee-february), a group that provides a 

forum for a diverse group of stakeholders to provide feedback to EPA on various issues related 
7

to pesticides. OPP held a teleconference for EPA’s Region 8 stakeholders (e.g., growers, crop 

consultants) on March 5, 2015 and met with representatives from the NAICC (National Alliance 

of Independent Crop Consultants) on April 22, 2015 to discuss EPA’s proposal in more depth. 

In March 2015, EPA initiated discussions with the Bt corn companies (via the ABSTC 

consortium group) on the proposed framework. Additional meetings with ABSTC were held 

throughout 2015 to further discuss changes to the terms and conditions of the CRW PIP 

registrations. Minutes from the meetings are in the public docket. Based on input from 

stakeholders, EPA modified aspects of the framework to address various stakeholder concerns, 

including input received during the open comment period. EPA’s discussions with ABSTC

ended with an agreement that was announced on February 18, 2016 [14].

The final agreement was incorporated into new terms and conditions for each “single toxin” Bt 

corn registration (i.e., those expressing one CRW trait) [5], and companies have also committed to 

implementing the provisions of the terms and conditions for “pyramided” products that express 

multiple CRW Bt traits. EPA will formally amend the terms and conditions of the pyramided 

products when they come up for renewal over the next several years. 

Lastly, EPA is working with the companies to transition out of single trait products into 

pyramided products over a several year period, which offers enhanced protection against 

resistance development.

E. Response to Public Docket Comments

EPA received a total of 87 comments relating to the Agency’s August 27, 2014 draft proposal to 

improve the resistance management program for corn rootworm and Bt corn. Of these 

comments, 71 specifically addressed the proposal, four comments expressed general opposition 

to EPA’s regulation of Bt corn, 11 voiced overall opposition to GMOs/agricultural 

biotechnology, and one was ambiguous. Commenters represented a variety of groups, including 

corn growers, state grower associations and farm bureaus, university extension entomologists, 

independent crop consultants, biotechnology companies and their industry group (ABSTC), nongovernmental organizations (including environmental and advocacy groups), state departments 

of agriculture, and the United States Department of Agriculture (USDA). Commenters addressed 

topics such as IPM stewardship, crop rotation, the use of soil-applied insecticide for CRW, 

resistance investigations, bioassays to determine resistance, and mitigation strategies for cases of 

resistance. In summary, EPA carefully reviewed and considered all public comments received 

and substantially revised its initial proposal to address those comments.

1) IPM Stewardship

Many of the comments received addressed the IPM stewardship aspect of EPA’s 

proposal. Commenters generally expressed support for IPM approaches for CRW resistance

management (21 comments), while also expressing a need for grower flexibility within IPM 

programs (32 comments). A number of commenters expressed opposition to “mandatory” crop 

rotation (24 comments) and overly prescriptive IPM adoption targets (7 comments). Others noted 

that growers/industry were already implementing IPM programs for CRW (10 comments). A few 
8

commenters (4 comments) cautioned that crop rotation would complicate IPM stewardship in 

areas with the rotation resistant corn rootworm variant. Additional commenters (6 comments) 

noted that there was limited or no availability of non-Bt corn seed varieties available to growers.

Agency Response: EPA addressed some of these concerns in its ultimate decision by 

moving away from the proposed, prescriptive regional IPM adoption targets, which had 

specified certain levels of crop rotation for areas based on risk of CRW resistance. The 

Agency believes that crop rotation with a non CRW host (such as soybean) is the most 

effective means of reducing the risk of CRW resistance development; however, EPA also 

recognizes the need for grower flexibility and realizes that not all growers can rotate to 

soybean. To address these concerns, EPA’s new CRW framework requires ABSTC and its 

member companies to work with growers to implement best management practices as 

supported by good IPM with the deployment of Bt corn for the purpose of corn rootworm 

control. The framework indicates that soybean rotation is strongly preferred as a BMP, but 

also provides additional options for other multi-year management plans including the use

of pyramided Bt corn, rotation of single Bt modes of action, and non-Bt corn with 

conventional CRW control (insecticides). It should also be noted that growers are not 

obliged to adopt measures that are not compatible with their current farming practices. 

ABSTC is mandated under the new framework to monitor IPM adoption via anonymous 

third party surveys, which will be submitted to the Agency on an annual basis.

2) Use of Soil Applied Insecticides for Control of Corn Rootworm on Bt Corn

Forty-eight comments addressed the soil-applied insecticide (SAI) use prohibition language with 

Bt corn in EPA proposal. Specifically, commenters opposed restrictions on SAI use with Bt corn 

(45 comments), while some were in support of EPA’s proposal (2 comments). Those opposed to 

SAI restrictions cited the need to maintain all available CRW controls, additional pests 

controlled by insecticides, economic considerations, and the benefits of SAIs in buttressing the 

efficacy of Bt corn and providing higher yields. The commenters recommending against the use 

of SAIs with Bt corn indicated it would hasten resistance to Bt, specifically if the Bt trait had 

previously failed in a field. One additional commenter stated that SAI use with single mode of 

action Bt corn could be justified but that it should not be needed for pyramided Bt corn.

Agency Response: EPA recognizes the need to maintain available CRW management tools

but remains concerned that SAI use with Bt corn can increase the risk of CRW resistance. 

Therefore, EPA changed the proposed language from a prohibition against the use of SAI 

in combination with Bt corn to a recommendation that growers not use SAI with Bt corn 

for CRW control “except in limited situations and in consultation with extension, crop 

consultants, and other local experts.” This language will be incorporated into the grower

educational materials for the single Bt corn products and pyramided Bt corn products.

3) Resistance Investigation

Public commenters who addressed the resistance investigation aspect of EPA’s proposal were 

generally in agreement that a random resistance monitoring program was not needed and that 

focusing on unexpected damage sites instead was more effective (3 comments). Several 

comments were supportive of scouting for unexpected damage in Bt corn using the Agency’s 
9

threshold criteria and implementing BMPs as a proactive response to unexpected damage to Bt 

corn (7 comments). However, some commenters cautioned that resources for scouting were 

limited (3 comments), and there were privacy concerns with unexpected damage reporting (3

comments). Some commenters expressed the need to standardize BMPs across industry but to 

keep them as recommendations (5 comments). The Agency’s proposed scouting thresholds for 

single and pyramided Bt corn were thought to be too low (1 comment) or too high and not 

proactive enough (1 comment).

Agency Response: Random sampling for CRW resistance monitoring purposes has proved 

ineffective; resistant corn rootworm populations were not detected with this approach but 

rather with sampling that occurred in UXD sites [1]. Accordingly, the Agency replaced the 

random sampling resistance monitoring program with a resistance monitoring program that 

focuses on unexpected Bt damage sites instead. EPA understands that cases of unexpected 

damage could be an indication of developing CRW resistance to Bt corn. Therefore, the 

Agency believes a standardized and proactive response to these cases is essential to early 

mitigation of potential resistance. Along these lines, EPA has adopted uniform root damage 

thresholds across industry for single Bt corn (>1.0 NIS, i.e., more than 1 node of roots 

removed) and pyramided Bt corn (> 0.5 NIS, i.e., more than 1⁄2 node of roots removed) as 

triggers for conducting investigations in damaged fields. EPA has also required that 

companies recommend that growers implement BMPs the following growing season in 

response to unexpected damage. These BMPs include tools for management of CRW, 

including crop rotation to soybean (preferred option), use of pyramided Bt corn, rotation of

single Bt modes of action, use of non-Bt corn, and conventional insecticide use. Biotech 

companies will provide reports to the Agency on unexpected damage cases at the county 

level for each State. To address potential privacy concerns, EPA has required that these 

reports not include any personally identifiable information related to growers. EPA also 

recognizes that scouting resources may be limited but has required the Bt companies to

coordinate responses to unexpected damage cases.

4) Bioassays

Three commenters recommended that EPA continue the use of diet bioassays alongside on-plant 

assays (3 comments). One commenter preferred a complete switch to on-plant assays. Several 

other commenters noted that bioassays for resistance determinations should meet criteria for 

successful resistance detection in terms of biological relevance, sensitivity, consistency, 

appropriate baselines, and control colonies (2 comments).

Agency Response: As mentioned above, the Agency replaced the random sampling 

resistance monitoring program with a resistance monitoring program that focuses on 

unexpected Bt damage sites instead. Population collections will be obtained from the site of 

damage during the year of UXD or the field and surrounding fields (if unable to collect that 

year), and root node injury will be assessed with a transect-sampling approach through the 

damaged location in the field of concern. On-plant assays are the Agency’s preferred 

approach for testing field collected populations for resistance to Bt because they can 

function as diagnostic tools (i.e., capable of clearly distinguishing resistant CRW 

populations from susceptible ones). EPA is concerned that current diet bioassay approaches 

lack the sensitivity to reliably detect resistance populations. Nonetheless, EPA is open to an 
10

improved diet bioassay that addresses the Agency’s goals of having a reliable diagnostic 

test to determine resistance. As part of the final CRW framework, EPA established criteria 

for resistance detection assays and required companies to consult with EPA on their assay 

approach prior to its use. Industry may continue to pursue a diet-based approach provided 

that improvements are made to the methodology and a resistant lab colony is used as a 

control to validate resistance conclusions.

5) Remedial Action

Several commenters noted that mitigation of resistance was a more realistic goal then 

remediation (4 comments). One commenter proposed to make crop rotation the primary tool to 

mitigate a resistant population because other approaches would be less effective, while other 

commenters recommended that mitigation plans should be flexible and not overly prescriptive (3 

comments). Six commenters noted that “beetle bombing” (i.e., use of conventional insecticides 

to kill adult corn rootworm and prevent egg laying) is not a preferred IPM method - especially 

not in response to unexpected damage; overuse could lead to pyrethroid resistance (the 

insecticide of choice against CRW). One commenter indicated that it was crucial for growers to 

obtain information regarding corn rootworm resistance developments. Additional commenters

noted that there were uncertainties with defining remedial action areas based on corn rootworm 

dispersal (2 comments), while others cited concerns about the feasibility of including multiple 

farms in a defined remediation area (3 comments).

Agency Response: The Agency agrees that mitigation is a more appropriate description of 

the response strategy for resistant populations than remediation and has included the term 

in the revised framework. The Agency recognizes that crop (soybean) rotation is the most 

effective tool to mitigate a resistant corn rootworm population and has indicated that it is 

the preferred mitigation action tool in the final framework. Furthermore, the Agency has 

incentivized industry to work with growers to use crop rotation in cases of unexpected 

damage to Bt corn so that the best mitigation action can occur before resistance is 

confirmed. EPA agrees with the comments about beetle bombing. In the finalized 

framework, beetle bombing is listed as the least preferred option to mitigate resistance 

because it can create resistance risks for conventional pesticides as well as environmental 

and human health effects. 

Regarding the mitigation action area, EPA defined the scope of this area as the “grower’s 

farming operation up to a 1⁄2 mile radius from the damaged site that produced the resistant 

population.” This distance was based on the typical life-time dispersal potential for CRW 

beetles. EPA recognizes the challenges of including multiple farming operations within this 

area. To address this concern, the agreed-upon framework requires the company with the 

resistance issue to inform its customers within the mitigation action area, as well as 

extension entomologists, crop consultants and other companies selling the same trait. In 

addition, EPA is looking to develop its own notification system to report incidents of 

resistance as well as unexpected damage in Bt corn. EPA believes the timely dissemination 

of information to affected stakeholders will allow growers to make informed decisions 

regarding CRW management. 
11

6) Other Comments and Recommendations

A number of commenters recommended that EPA consider raising the refuge requirements for 

Bt corn to 50% for single traits (from the currently required 20%) and 20% for pyramided 

varieties (from the current 5%) (6 comments). Additional commenters urged EPA to increase 

grower education/training for growers (7 comments). Several commenters suggested that it may 

be too late to address IRM in the Corn Belt and that the Agency should instead focus on “fringe” 

areas of the Corn Belt where the Bt traits are still effective (2 comments). Others comments 

recommended EPA incentivize crop rotation and IPM activities (2 comments), offer expanded 

crop rotation options (e.g., longer rotations with pyramids) (2 comments), and restrict the use of 

single trait Bt corn products (in favor of pyramids) (2 comments).

Agency Response: EPA believes that the finalized framework will greatly enhance the 

durability of Bt corn at the current refuge levels. Nevertheless, EPA recognized the 

concern raised about the current refuge requirements and, in cases of confirmed resistance, 

the framework requires that companies increase the refuge for any pyramids with the 

affected trait to 20% in the resistance mitigation action area.

EPA agrees that that grower education is an essential aspect of IRM. The registrantimplemented grower education outreach will be a major component of the IPM 

stewardship program that is a required part of the finalized framework to improve CRW 

IRM. As part of the stewardship program, companies must encourage growers to engage 

in multi-year crop rotation strategies designed to reduce selection pressure for resistance. 

These rotational strategies can include planting a non-CRW host (e.g., soybean), 

pyramided Bt corn products, other Bt corn products with different modes of action, and/or 

non-Bt corn. EPA believes the new framework establishes incentives for industry to 

promote crop rotation to a non-host crop such as soybean in cases of unexpected damage 

or resistance. If growers rotate to a non-host crop in such cases, the affected area is 

considered “mitigated” and no further action will be required of the companies.

F. Summary of Final Agreement between EPA and ABSTC

In response to evidence that corn rootworm has evolved resistance to some single trait Bt 

products, EPA announced the adoption of new, more protective requirements designed to delay 

corn rootworm resistance to genetically engineered Bt corn on February 18, 2016 [5][14]. The 

final framework consists of several improvements to the previous corn rootworm resistance 

management paradigm that were in part based on an independent science peer review, a letter to 

EPA from corn rootworm experts, as well as public comments to EPA’s docket. These measures 

will be included as registration terms for Bt corn products and include the following:

1. IPM Stewardship Program

Companies supplying Bt corn are required to implement a stewardship program designed to 

reduce selection pressure by encouraging growers to implement a multi-year crop rotation 

strategy with the use of corn rootworm protected Bt corn. Implementation of the IPM strategy 

can include grower education initiatives or incentives; and outreach to extension and consultant 

groups.
12

To address concerns about the potential for SAI use with Bt corn to exacerbate resistance 

development, EPA is requiring that grower educational materials provided as part of the 

stewardship program include language stating that SAIs with single Bt corn control is not 

recommended for the control of corn rootworm except under limited circumstances and in 

consultation with extension, crop consultants or other local experts” and, for pyramided 

products, SAI use should not be necessary for CRW control with pyramided CRW trait Bt corn

products. Each Company must submit a report to EPA annually documenting activities under the 

IPM stewardship program including an anonymous survey of grower practices, and adoption of 

various IPM tools such as crop rotation.

2. Investigation of Reports of Unexpected Damage (UXD) by Corn Rootworm: 

Performance Inquiries

When companies become aware of field failures, it is important to EPA that those fields and 

populations of rootworm are investigated to determine what caused the damage. EPA is requiring 

that companies investigate “performance inquiries” from corn growers and determine if the 

damage is attributed to corn rootworm feeding and exceeds a root damage threshold based on 

Node Injury Score (>1.0 for single Bt corn; >0.5 for pyramided Bt corn). If the NIS trigger is 

exceeded in a UXD field, companies must collect insect from the damaged site and test those 

insects for resistance using a bioassay approach described in detail in the terms and conditions, 

and summarized in section 3 below. 

For fields meeting the criteria above, companies must review the CRW management history with 

growers and provide corn rootworm management recommendations, including an assessment of 

corn fields with similar trait(s) adjacent to the affected corn field that are managed by the same 

grower. In those fields, companies should also discourage the use of single-trait products 

containing the affected CRW trait and encourage the following recommended management 

options: 

• Primary option: Rotation to a non-host crop (e.g., soybean); 

• Secondary options: Use of pyramided Bt corn with multiple CRW traits, use of a 

different single corn rootworm Bt trait, use of non-Bt corn or non-CRW protected Bt 

corn (with conventional insecticides); 

• Tertiary option: If additional pest management need is determined beyond the 

secondary options, additional CRW control tools including soil insecticides, seed 

applied insecticides, and chemigation can be used.

• If a UXD field is rotated to a non-CRW host crop (e.g., soybean), the area will be 

considered mitigated and no further actions will be required by the companies for the 

UXD case.

Each Company must submit an annual report detailing activities related to investigations of UXD 

fields from the most recent (previous) corn growing season, final disposition of UXD fields from 

previous seasons, and bioassays results if crop rotation was not implemented. UXD reports must 

be submitted by county and state, but must exclude sensitive business and customer information.
13

3. Investigation of Populations of Concerns: Resistance Detection Assays

In order to definitively determine whether populations of rootworm causing unexpected damage 

are resistant, EPA is requiring that these populations be collected, and also tested. EPA is 

requiring that companies conduct investigation of all CRW populations collected as part of the 

performance inquiry process described above. These investigations must include the use of an 

EPA-approved bioassay to determine if the sampled populations are resistant. The employed 

assay must be able to function as a diagnostic tool capable of distinguishing resistant populations 

from susceptible ones. See the Terms and Conditions for additional details on the criteria for a 

population to be considered resistant.

EPA is requiring mitigation, as described in the next section below, for any corn rootworm 

population that meets the resistance criteria. If the results of the bioassays are inconclusive, 

companies must collect and assay populations from the UXD field/area for another year. 

4. Mitigation of CRW Populations Meeting EPA’s Resistance Criteria 

It is important to EPA that affected stakeholders be made aware of the detection of resistance and 

that measures are put in place to prevent documented resistance from spreading. Therefore, for 

any resistant population, EPA is requiring that companies take the following steps;

a) Inform EPA of the bioassay results;

b) Notify state extension agents and crop consultants within the county where 

resistance was identified of resistance detection in their county and the trait(s) 

affected;

c) Within a 1⁄2 mile radius around the resistant site, EPA is requiring that companies

i. Inform affected growers and other registrants holding registrations for 

the affected trait prior to finalizing growers’ seed orders the following 

year. The company must also inform neighboring growers if those 

growers are also customers of the company. Information shared must 

include identification of the county in which resistance was detected 

and the trait(s) affected; 

ii. Discontinue sales and planting of single trait product containing the 

compromised trait until resistance has been mitigated; 

iii. Monitor the resistant population until resistance is mitigated (as long 

as the grower remains a customer of the company); 

iv. Require that pyramids containing the resistant trait and sold and 

planted in the area receive a 20% refuge until resistance is mitigated; 

v. Encourage the use of “Mitigation Practices” including crop rotation, 

use pyramids, and other best management practices.
14

5. Annual Reporting

Each company must submit the following annual reports to allow EPA to review the status of 

this new CRW mitigation program:

a) IPM Stewardship Program: Activities conducted under the IPM stewardship 

program, including an anonymous survey of grower practices, adoption levels of the 

various crop rotation options (if employed) and other elements of the stewardship 

program, on or before January 31st of each year.

Unexpected Damage Investigations: Activities related to investigations of unexpected damage 

(UXD), including number and location of UXD cases, insect sampling, bioassays, and final 

disposition of UXD fields from the most recent and previous corn growing seasons, on or before 

November 30th of each year.

G. Transition Plan from Single-Traited Bt Corn to Pyramided Bt Corn

The first single trait Bt corn for the control of corn rootworm was registered in 2003, while the 

first pyramided Bt corn (expressing two or more traits to a pest) was approved by EPA in 2009.

Research indicates that single Bt traits deployed concurrently with pyramided Bt products will 

hasten resistance development to pyramids [16]. This is of concern to the Agency, especially in 

the context of present corn rootworm resistance to Cry3Bb1 and cross-resistance between 

Cry3Bb1 and mCry3A expressing corn [12]. EPA is further concerned because there are only a 

limited number of Bt traits available to growers to manage corn rootworm. The Agency views 

the stewardship for pyramided PIP corn as a high priority to maintain the usefulness of these 

products for growers for as long as possible.

Although EPA and the biotech companies have reached an agreement on the improved 

framework for Bt corn targeting corn rootworm, the improved stewardship program will be

strengthened by limiting the planting of single Bt corn rootworm protected corn over time.

However, EPA also recognizes the needs of farmers and understands that growers rely on

specific corn hybrids for which pyramided varieties may not be immediately available. 

Therefore, EPA is working with the companies to transition out of single trait products over time 

into the pyramided products while taking into consideration the needs of the farmers. EPA has 

extended the registrations of the single trait products through 2019 with yearly reductions in 

acreage planted to allow time for the transition to occur and will consider further extensions of 

the single trait products on a case-by case basis by imposing, for example, acreage caps,

geographic restrictions, and/or other IRM-related mitigation. By 2020, almost all Bt corn 

targeting corn rootworm and planted in the US will be of the pyramided variety.

H. Conclusion

EPA firmly believes that the new CRW resistance management framework will result in an 

improved stewardship and resistance monitoring program for Bt corn. The new framework is the 

result of a public and transparent process involving a wide range of stakeholders including 
15

academic researchers [8] [14]

, a Scientific Advisory Panel [3], public interest groups and the public 

[4]

. Its aim is to delay resistance in corn rootworm to Bt biotech traits for as long as possible, 

particularly for the pyramided products, allowing growers to effectively and safely manage corn 

rootworm with the help of these tools. The framework, therefore, provides benefits to agriculture 

and growers (reduced use of conventional pesticides and exposure to humans, environment, and 

non-target species), biotech companies, and the public as well as the environment by extending 

the effectiveness of these beneficial products.

I. References

1. Gassmann, A. J., J. L. Petzold-Maxwell, R. S. Keweshan, and M. W. Dunbar. 2011.

Field-evolved resistance to Bt maize by western corn rootworm. PLoS ONE e22629.

2. US EPA [United States Environmental Protection Agency]. 2013. White paper on corn 

rootworm resistance monitoring for Bt Plant-Incorporated Protectants. Report from OPP’s 

IRM team to the 2013 Scientific Advisory Panel in the Biopesticide and Pollution Prevention 

Division. Docket number: EPA-HQ-OPP-2013-040;

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2013-0490-0031

3. US EPA FIFRA [United States Environmental Protection Agency Federal Insecticide, 

Fungicide and Rodenticide Act] Scientific Advisory Panel. 2014. Transmittal of Meeting 

Minutes of the FIFRA Scientific Advisory Panel Meeting Held on December 4-6, 2013 on 

scientific uncertainties associated with corn rootworm resistance monitoring for Bt corn. 

Docket number: EPA-HQ-OPP-2013-0490; 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2013-0490-0044

4. Draft Proposal to ABSTC to Improve Insect Resistance Management for Bt Corn.

Docket number: EPA-HQ-OPP-2014-0805; 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2014-0805-0002

5. Terms and Conditions of Bt Corn Registrations. 2016. Docket number: EPA-HQ-OPP2014-0805; http://www.regulations.gov/#!searchResults;rpp=25;po=0;s=EPA-HQ-OPP2014-0805;fp=true;ns=true

6. Andow, D. A., S. G. Pueppke, A. W. Schaafsma, A. J. Gassmann, T. W. Sappington, L. 

J. Meinke, P. D. Mitchell, T. M. Hurley, R. L. Hellmich and R. P. Porter. 2015. Early 

detection and mitigation of resistance to Bt maize by western corn rootworm (Coleoptera: 

Chrysomelidae). J. Econ. Entomol., Vol. 109(1): 1-12.

7. Martinez, J. C. and M. A. Caprio. 2016. IPM use with the deployment of a non-high dose 

Bt pyramid and mitigation of resistance for western corn rootworm (Diabrotica virgifera 

virgifera). Env. Entomol., http://ee.oxfordjournals.org/cgi/reprint/nvw015?
16

ijkey=RSoVuMMLBzsAjrX&keytype=ref 

8. Gassmann, A. J. 2012. Field-evolved resistance to Bt maize by western corn rootworm: 

predictions from the laboratory and effects in the field. J. Invertebr. Pathol., Vol. 110: 287-

293.

9. Gassmann, A. J., J. L. Petzold-Maxwell, R. S. Keweshan, and M. W. Dunbar. 2012.

Western corn rootworm and Bt maize: challenges of pest resistance in the field. GM Crops 

Food: 3: 235-244.

10. Gray, M. E. 2012. Continuing Evolution Confirmed of Field Resistance to Cry3Bb1 in 

Some Illinois Fields by Western Corn Rootworm. The Bulletin, No. 20(2). 

11. Wangila, D. S., A. J. Gassmann, J. L. Petzold-Maxwell, B. Wade French, and L. J. 

Meinke. 2015. Susceptibility of Nebraska Western corn rootworm (Coleoptera: 

Chrysomelidae) Populations to Bt corn events. J. Econ. Entomol., Vol. 108(2): 742-751.

12. Gassmann, A. J., J. L. Petzold-Maxwell, E. H. Cliffton, M. W. Dunbar, A. M. 

Hoffmann, D. A. Ingber, and R. S. Keweshan. 2014. Field-evolved resistance by western 

corn rootworm to multiple Bacillus thuringiensis toxins in transgenic maize. PNAS, Vol. 

111(14): 5141-5146.

13. Porter P., E. Cullen, T. Sappington, A. Schaafsma, S. Pueppke, D. Andow, J. Bradshaw, 

L. Buschman, Y. J. Cardoza, and C. DiFonzo. 2012. Comment submitted by Pat Porter 

North Central Coordinating Committee NCCC46 and other corn entomologists. 

https://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2011-0922-0013

14. US EPA [United States Environmental Protection Agency]. 2016. OPP Update: New 

requirements to address corn rootworm resistance. Released on February 18, 2016. 

https://www.epa.gov/pesticides/new-requirements-address-corn-rootworm-resistance-bt-corn

15. Oleson, J D, YL Park, T M Nowatzki, and J Tollefson. 2005. Node-injury scale to 

evaluate root injury by corn rootworm (Coleoptera: Chrysomelidae). J. Econ. Entomol., Vol. 

98(1): 1-8.

16. Zhao, J. Z., J. Cao, H. L. Collins, S. L. Bates, R. T. Roush, E. D. Earle, and A. M. 

Shelton. 2005. Concurrent use of transgenic plants expressing a single and two Bacillus 

thuringiensis genes speeds insect adaptation to pyramided plants. Proc. Natl. Acad. Sci.; 

Vol. 102(24): 8426-8430.