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
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
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
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
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
• 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.