Inheritance and Fitness Costs of Bt

Resistance for Field-Derived Strains

of Western Corn Rootworm

(Diabrotica virgifera virgifera LeConte)

David A. Ingber1, Graham P. Head2, Aaron J. Gassmann1

1Department of Entomology, Iowa State University, Ames, IA 50011

2Monsanto Company, St Louis, MO 63167

© Marlin E. Rice

western corn

rootworm neonate

Bt Plants Refuge

Refuge Strategy

RR = resistant insect

SS = susceptible insect

RS = heterozygote insect

• Gould 1998

• Tabashnik et al. 2003

• Gassmann et al. 2011

Bt Plants Refuge

RR SS

Refuge Strategy

• Gould 1998

• Tabashnik et al. 2003

• Gassmann et al. 2011

Bt Plants Refuge

RR SS

RS

Refuge Strategy

• Gould 1998

• Tabashnik et al. 2003

• Gassmann et al. 2011

Bt Plants Refuge

RR SS

RS

RS

RS

Refuge Strategy

• Gould 1998

• Tabashnik et al. 2003

• Gassmann et al. 2011

Bt Plants Refuge

RR SS

RS

RS

RS

Refuge Strategy

• Gould 1998

• Tabashnik et al. 2003

• Gassmann et al. 2011

Fitne

ss

RR SS

Fitness Costs

Non-Bt

• McKenzie and

Batterham 1994

• Gassmann et al. 2009

• Carriere et al. 2010

Bt Plants Refuge

RR SS

RS

RS

RS

Refuge Strategy

• McKenzie and

Batterham 1994

• Gassmann et al. 2009

• Carriere et al. 2010

Bt Plants Refuge

RR SS

RS

RS

RS

Refuge Strategy

• McKenzie and

Batterham 1994

• Gassmann et al. 2009

• Carriere et al. 2010

Hypotheses

For a non-diapausing strain of WCR with

field-derived Cry3Bb1 resistance:

1.The genetic inheritance of Bt resistance

will be non-recessive – (Meihls et al. 2008, Tabashnik and Gould 2012)

2.Fitness costs will be present – (Gassmann et al. 2009, Carriere et al. 2010)

Hopkinton Strain

• Sampled from two fields in 2010 (Gassmann et al. 2011)

• Planted continuously with Cry3Bb1

corn for 7 years

• Sampled from two fields in 2010 (Gassmann et al. 2011)

• Planted continuously with Cry3Bb1

corn for 7 years

Hopkinton Strain

• Sampled from two fields in 2010 (Gassmann et al. 2011)

• Planted continuously with Cry3Bb1

corn for 7 years

• 53 males collected and crossed

with 356 virgin females from a

non-diapausing, susceptible strain

(susceptible strain)

Hopkinton Strain

• Sampled from two fields in 2010 (Gassmann et al. 2011)

• Planted continuously with Cry3Bb1

corn for 7 years

• 53 males collected and crossed

with 356 virgin females from a

non-diapausing, susceptible strain

(susceptible strain)

• Selected on Cry3Bb1 corn twice

followed by backcrossing, then

selected a third time

Hopkinton Strain

• Sampled from two fields in 2010 (Gassmann et al. 2011)

• Planted continuously with Cry3Bb1

corn for 7 years

• 53 males collected and crossed

with 356 virgin females from a

non-diapausing, susceptible strain

(susceptible strain)

• Selected on Cry3Bb1 corn twice

followed by backcrossing, then

selected a third time

• Reared in the laboratory for 19

generations

Hopkinton Strain

LC50: 11.74 µg/cm2 95% FL: 4.48 to 19.11 µg/cm2

LC50: 153.48 µg/cm2

95% FL: 104.32 to 227.84 µg/cm2

LC50: 11.74 µg/cm2 95% FL: 4.48 to 19.11 µg/cm2

LC50: 153.48 µg/cm2

95% FL: 104.32 to 227.84 µg/cm2

13.1

Hypotheses

For a non-diapausing strain of WCR with

field-derived Cry3Bb1 resistance:

1.The genetic inheritance of Bt resistance

will be non-recessive

2.Fitness costs will be present

Measuring Inheritance With

Reciprocal Crosses

R♀ R♂

F1

S♀ S♂

F1

R♀ S♂

F1

S♀ R♂

F1

Survival to Adulthood

R♀ * S♂

S♀ * R♂

5.4

Inheritance

Inheritance is between additive and recessive

0 0.5 1

0.373

Recessive Dominant Additive

• Tabashnik et al. 2004

Hypotheses

For a non-diapausing strain of WCR with

field-derived Cry3Bb1 resistance:

1.The genetic inheritance of Bt resistance

will be non-recessive

2.Fitness costs will be present

Fitness Costs

Costs measured:

• Development rate • Date of emergence

• Survival to adulthood • Percent emergence

• Head capsule width

• Egg viability • Percent hatch

• Fecundity • Eggs per week

• Total lifespan

Fitness Costs

Cost Measured Effects df F value P value

Development rate Strain 1,15 0.04 0.8512

Proportion survival Strain 1,30 0.92 0.3454

Head capsule width Strain

Sex

Strain*Sex

1,15

1,30

1,30

1.26

31.18

0.51

0.2784

< 0.0001

0.4799

Egg viability Strain 1,29 3.12 0.0879

Eggs per week Strain

Week

Strain*Week

1,15

12,360

12,360

0.50

67.12

0.84

0.4910

< 0.0001

0.6134

Adult lifespan Strain

Sex

Strain*Sex

1,15.231

1,31.888

1,31.888

0.29

2.43

8.57

0.5954

0.1293

0.0063

Fitness Costs

Cost Measured Effects df F value P value

Development rate Strain 1,15 0.04 0.8512

Proportion survival Strain 1,30 0.92 0.3454

Head capsule width Strain

Sex

Strain*Sex

1,15

1,30

1,30

1.26

31.18

0.51

0.2784

< 0.0001

0.4799

Egg viability Strain 1,29 3.12 0.0879

Eggs per week Strain

Week

Strain*Week

1,15

12,360

12,360

0.50

67.12

0.84

0.4910

< 0.0001

0.6134

Adult lifespan Strain

Sex

Strain*Sex

1,15.231

1,31.888

1,31.888

0.29

2.43

8.57

0.5954

0.1293

0.0063

Hypotheses

For a non-diapausing strain of WCR with

field-derived Cry3Bb1 resistance:

1.The genetic inheritance of Bt resistance

will be non-recessive

2.Fitness costs will be present

Hypotheses

For a non-diapausing strain of WCR with

field-derived Cry3Bb1 resistance:

1.The genetic inheritance of Bt resistance

will be non-recessive – Supported: h = 0.373; Inheritance is between

additive and recessive

2.Fitness costs will be present – Rejected: No fitness costs identified

Bt Plants Refuge

SS

RS

RR

RS

RS

Implications

Implications

Bt Plants Refuge

RR SS

RS

RS

RS

Survival

Implications

Bt Plants Refuge

RR SS

RS

RS

RS

Survival RR

RR

RR

RS

RS

RS

• Repeating experiments with a second

resistant strain with field-derived alleles

• Currently collecting and analyzing data

Current Direction

Acknowledgments Richard Hellmich and Nick Lauter

Bruce and Vicki Lang

Jennifer Petzold-Maxwell

Amanda Hoffmann, Eric Clifton, Mike Dunbar, Ryan

Keweshan, and Chris Dojutrek

Renato Horikoshi

Sean Bradley, Yichao Dou, Ouma Amadou, and David Tirado

This research was supported by the Monsanto Company and by

Biotechnology Risk Assessment Grant Program competitive grant no. 2012-

33522-20010 from the USDA National Institute of Food and Agriculture.

Rearing Procedure

Diet Based Bioassays

Susceptible

Resistant