Dec. 4-6, 2013

DuPont Pioneer SAP Comments: 

Corn Rootworm Resistance 

Monitoring

Clinton D. Pilcher, Ph.D. 

DuPont Pioneer
 

2

Challenges

Science

Solutions

Deliver

Collaboration

Growers, Industry

Academics, Regulators
 

3

Corn Rootworm (CRW) Management 

and Monitoring at Pioneer

Proactive Management

Unexpected Damage (UXD) Process

Sub-lethal Seedling Assay (SSA)

• Dr. Analiza Alves
 

4

Managing and Monitoring

Time

Resistance Allele Frequency

0.1

0.5

1.0

• Best Management Practices (BMPs)

• Management Based on “Field History”

• Integrated Refuge & Pyramids

• External Education & Outreach

• UXD Process

Proactive Reactive
 

5

Rootworm 

& Wind 

Damage 

Aug 28, 2001

Photo: Alex Woodall

DuPont Pioneer

Kamrar, IA

1999 – Soybeans

-23 bu/a

-32 bu/a

Know the Field History for BMPs
 

6

UXD Process and Characterization

Year 0 Year 1 Year 2

Grower Call

Field Evaluation

Adult Collection

Thresholds Met = Characterization 

Farm-Wide BMPs

Standardized Assays (SSA & GH)

Thresholds Met = Characterization

Adult Collection  Research

Stakeholder Communication

Assays

Confirmation
 

7

Regulation Should Encourage:

Uniformity in UXD process

Technical collaboration/coordination 

among stakeholders

Practical solutions for 

growers and registrants

Sound science and 

knowledge sharing
Dec. 4-6, 2013

DuPont Pioneer SAP Comments: 

Corn Rootworm Resistance 

Monitoring

Analiza Alves, Ph.D. 

DuPont Pioneer
 

9

Diet bioassay

• Sanitation

• Low sensitivity to toxins

• Discriminating concentrations are impractical

Other approaches 

• On-plant assays may offer 

increased sensitivity

• Sub-lethal Seedling Assay (SSA)

Challenges of Rootworm Resistance 

Monitoring & Detection
 

10

59122 Effect is More Chronic Than Acute

Susceptible larvae extracted after 17 days of exposure

Initial feeding does not result in 

direct mortality

Isoline 59122
 

11

Pioneer Sub-lethal Seedling Assay (SSA) 

Larval Development Distribution

Proportion of Population

59122

Isoline

Output: Mean instar ratio = Mean instar Bt

 Mean instar non-Bt

Instar

Source: Nowatzki, et al. 2008
 

12

Initial Observations on CRW Field 

Populations SSA Trials

Variability of SSA results from field CRW populations 

higher than expected

Potential loss of insects to pupation 

Need for better separation between resistant and control 

laboratory population

SSA Further Optimized
 

13

Optimization Results – Larval Recovery Recovery Rate (%)

– Exposure Length (oC Degree Days) +

Shorter exposure increases insect recovery 

Isoline, 500 eggs

Isoline, 1000 eggs

Treatments

59122, 500 eggs

59122, 1000 eggs

Initial 

SSA

56% increase 

in larval 

recovery
 

14

Optimization Results – Instar Means

Instar mean

Shorter exposure increases treatment separation

– Exposure Length (oC Degree Days) +
 

15

Improvements – Data Analysis

Mean Instar Ratio

Mean instar Bt

Mean instar non-Bt

Percent 3rd Instar Ratio

Percent 3rd instar Bt

Percent 3rd instar non-Bt
 

16

0.15 0.95

Percent 3rd Instar Ratio

RR lab colony

Mean Instar Ratio

Increased separation between lab resistant and field 

monitoring populations

Improvements – Data Analysis

% %

0.687 0.987
 

17

Assay Characterization for CRW 

Resistance Assessments

On-plant assays to assess resistance against 

59122 (Cry34/35) and Pioneer experimental 

event (mCry3A)

• SSA

• Greenhouse efficacy trial
 

18

SSA: % Larval Return 

59122-SS 59122-RR mCry3A-SS mCry3A-RR

Data suggest mortality is indicative of 

susceptibility for mCry3A*

Larval recovery on 59122 (Cry34/35) 

treatment is not informative

Event: 59122 mCry3A* Isoline 59122 mCry3A* Isoline 59122 mCry3A* Isoline 59122 mCry3A* Isoline

* Pioneer experimental event
 

19

SSA: Mean Instar Ratio

59122-SS 59122-RR mCry3A-SS mCry3A-RR

Instar assessment aligns with resistance development

Event: 59122 mCry3A* 59122 mCry3A* 59122 mCry3A* 59122 mCry3A* Diff. between trts –

+

* Pioneer experimental event
 

20

High NIS May Not Mean Resistance 

Infest Rate Low High

Know how a trait responds in an assay!

Isoline

Single 

CRW 

events

Median Root Rating 

(0-3 Node Injury Score)

Greenhouse Root Efficacy Bioassay
 

21

Summary Remarks

EPA has recommended on-plant assays for CRW 

resistance monitoring 

On-plant assays have the capability of detecting 

CRW resistance

Result interpretation is event specific

Assay characterization and 

validation are necessary