NRCS and IPM WORKING GROUP TELECONFERENCE DECEMBER 6, Resistance to Bt corn by western corn rootworm in the U.S. corn belt

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1 NRCS and IPM WORKING GROUP TELECONFERENCE DECEMBER 6, 2013 Resistance to Bt corn by western corn rootworm in the U.S. corn belt Eileen Cullen, Extension Entomologist University of Wisconsin - Extension cullen@entomology.wisc.edu The U.S. Corn Crop Planted acreage 96.4 million acres, up 5 % from 2011 and highest in U.S. since More than one-third to livestock feed, 40% to ethanol (ethanol + distillers grains) and 13% exported. Remainder to food and beverage production. 2012: 67% of all corn planted contained a Bt trait (USDA ERS 2012) Sources: USDA National Agricultural Statistics Service and Reuters,

2 Bt Corn Adoption in U.S. First Bt CB trait (Cry1Ab) commercialized in 1996; first Bt CRW trait (Cry3Bb1) in By 2009, 85% of U.S. corn was a biotech variety (transformed for herbicide tolerance, insect tolerance, or both). Of the 85% nearly half (46%) were stacked varieties containing both herbicide and Bt insect tolerance traits (USDA NASS 2010) 2012: 67% of all corn planted contained a Bt trait (USDA ERS 2012) Western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) Annual Reviews 2

3 Metcalf s Billion-Dollar Pest (1986) Root-feeding larvae. Decrease shoot biomass accumulation. Direct yield impact. Change composition of plants and grain. Reduce leaf CO2 assimilation and photosynthetic rate. Difficult to harvest lodged plants. Impressive history of adaptation Resistance to the organochlorine insecticide aldrin (Ball and Weekman 1963) Resistance to adult control measures methyl-parathion (organophosphate) and carbaryl (carbamate) (Meinke et al. 1998) Resistance to crop rotation in the western corn rootworm attributed to loss of ovipositional fidelity to corn (Levine et al. 2002, Cullen et al. 2008, Gray et al. 2009) 3

4 Insect Resistance Management IRM plan required by EPA for Bt corn registration to preserve long-term viability of plant incorporated protectants (PIPs) and microbial Bt sprays. Refuge (areas within or close to a field of the Bt corn where non-bt corn is planted). Refuge percentage and configuration Historically a 20% structured refuge High Dose/Refuge Strategy IRM assumptions as modeled for Bt European corn borer-protected corn. 1. Protein expressed in plant tissue at high dose 2. Resistance is inherited recessively 3. Random mating occurs 4. Initial resistance alleles are rare 5. Fitness costs are associated with resistance Sources: Gould 1998; Glaser and Matten

5 Keeping track of Bt traits Different combinations of traits have different refuges Structured (rows, block) or in-the-bag Understand Bt CRW traits to manage corn rootworm resistance Bt corn rootworm (CRW) traits Cry3Bb1 (MON863) YieldGard in 2003 Cry3Bb1 increased from 0.49 million acres in 2003 to 29.6 million acres by 2008 Cry34/35Ab1 Herculex (DAS ) in 2005 mcry3a (MIR604) Agrisure in 2006 ecry3.1ab (5307) Agrisure Duracade in

6 Stacked and Pyramided Traits Stacked Bt traits Pyramided Bt traits Western CRW Resistance to Bt Corn Field-evolved CRW resistance to Bt toxin Cry3Bb1 has been confirmed by on-plant bioassays in the peer-reviewed scientific literature for 11 populations in Iowa. In each of these cases, fields had been planted to the same single Bt rootworm trait for at least 3 consecutive years, and as many as 7 consecutive years. 6

7 Lafayette Co. WI July 2013 VT3P RIB 2 nd year corn Early May plant date in 2012 Corn-soybean rotation for many years prior to corn-corn Images courtesy of Ted Bay, UW-Extension Grant and Lafayette Cos. Rate corn roots and confirm Bt hybrid Checking rootworm Bt corn plants in La Salle County, IL, for expression of the Cry3Bb1 protein (AgraStrip GMO TraitChek, Romer Labs Technology, Inc. Newark, DE). Sept. 13, Images courtesy of Mike Gray, University of Illinois 7

8 Collect beetles from problem field Cullen Lab Research: 2,000+ beetles collected Rear Beetles in Laboratory Cullen Lab Research: 250,000 eggs obtained in the lab! 8

9 Eggs in cold storage before on-plant bioassays with Bt and non-bt corn WI CRW eggs sent to USDA ARS, Brookings, SD Eggs in cold storage for 5 months minimum for diapause Followed by on-plant bioassays (Bt corn vs. non-bt corn) Do these CRW survive at higher rates on Bt Cry3Bb1 corn? Other Bt trait corn? Results will tell us if this is a resistant population (2014) Figure 2. Survival of western corn rootworm on Bt and non-bt maize. Gassmann AJ, Petzold-Maxwell JL, Keweshan RS, Dunbar MW (2011) Field-Evolved Resistance to Bt Maize by Western Corn Rootworm. PLoS ONE 6(7): e doi: /journal.pone

10 Figure 3. Correlation analysis for corrected survival of western corn rootworm. Gassmann AJ, Petzold-Maxwell JL, Keweshan RS, Dunbar MW (2011) Field-Evolved Resistance to Bt Maize by Western Corn Rootworm. PLoS ONE 6(7): e doi: /journal.pone Adults collected from two problem fields in NW and NC Illinois during 2011 growing season. Severe lodging, root pruning, continuous corn, reliance on single Bt CRW trait Cry3Bb1 Bioassays on progeny at ISU revealed the populations are resistant to Cry3Bb1 and no crossresistance to Cry34/35Ab1). Gray,

11 Widespread field-evolved resistance of western CRW to Bt corn is a threat Bt CRW traits are low dose (high dose for ECB) Lack of substantial fitness cost to wcrw for developing resistance to Bt trait Mating may not be random for wcrw in Bt fields (beetles from Bt plants can mate with beetles from other Bt plants rather than refuge plants) Resistance allele frequency in wcrw field populations higher than expected Insufficient planting of refuges prior to RIB products IRM Compliance in U.S. Corn Belt Bt Trait Center for Science in the Public Interest (CSPI), 2011 Refuge Size Refuge Distance Bt Corn Borer ( ) Over 90% 96% Bt Corn Borer (2008) 78% 88% Bt Rootworm (2006) 89% 82% Bt Rootworm (2008) 74% 63% Bt Stacked Traits (2006) 78% 92% Bt Stacked Traits (2008) 72% 66% Data based on industry reports submitted to EPA Mean compliance over all three categories: 74% for size and 73% for distance Est million acres in the U.S. not in compliance Approx. three out of four U.S. corn growers do comply in this survey 11

12 Bt corn with at-plant insecticide? Node injury score: 0 3 nodes of roots pruned NIS of 1.0 generally results in 15.2% % yield decrease (Tinsley et al. 2013: J. Appl. Entomol.) Non-Bt Check VT3P (RK 585) Treatment VT3P (RK 585) + Capture LFR Herculex RW (P9675 AMRW) Herculex RW (P9675 AMRW) + Capture LFR Node-Injury Score 0.80 a 0.01 b 0.00 b 0.00 b 0.00 b *No difference in root node injury scores for Bt vs. Bt + insecticide Data collected by B. Jensen, UW IPM Bt corn + at-plant insecticide? Illinois Study (Steffey and Gray 2007) Bt (Cry3Bb1), NIS = 0.84 Bt (Cry3Bb1) + Counter 15G, NIS = 0.07 *Root feeding reduced at only 1 of 3 locations Iowa Study (Gassmann 2012) Bt (Cry3Bb1) Bt (Cry3Bb1) + Force 3G Bt (Cry3Bb1) + Aztec 2.1G *Root feeding significantly reduced in fields with resistant CRW populations 12

13 Bt + Insecticides and IRM? Mortality achieved by soil insecticides may be too low to have a meaningful effect on resistant CRW in the population Bt corn delayed adult CRW emergence by 12 days relative to non-bt corn Bt corn + insecticide emerged even later Difference in timing of emergence in refuge vs. Bt corn can hinder random mating a requirement for IRM Petzold-Maxwell et al. 2013: J. Econ. Entomol. *Insect Resistance Management Rotate to soybean or nonhost crop Non-Bt hybrid with soil insecticide Alternate Bt corn modes of action (rotate traits) Pyramided Bt corn with multiple CRW traits Adult suppression for 1-2 seasons if rotation is not an option or pyramids not used (soil insecticide to non-bt corn, foliar adulticide) Long term integrated approach based on scouting and multiple tactics. Cullen et al. 2013: J. Integrated Pest Mgt. 13

14 Effectively dealing with the challenge of field-evolved resistance to Bt corn by western corn rootworm will require better adherence to the principles of integrated pest management. Photo: Mark Steil, Minnesota Public Radio, Quote: Gassmann et al