More Corn Rootworm Resistance To Bt Corn Reported In Illinois

With the addition of three more counties, a total of five Illinois counties have now reported confirmed cases of field-evolved resistance to Bt corn (Cry3Bb1 protein) by Western corn rootworm, and a University of Illinois entomologist said now is the time to move forward aggressively with integrated pest management (IPM) strategies, according to the Illinois Ag Connection.

In August 2012, in cooperation with an Iowa State University lab, Mike Gray said he confirmed resistance in Henry and Whiteside counties in northwestern Illinois. Working with Joe Spencer of the Illinois Natural History Survey and utilizing single-plant bioassays with larvae collected last summer, Gray said resistance to the Cry3Bb1 protein has now also been confirmed in McDonough, Mercer, and Sangamon counties.

The suspected Bt-resistant larvae collected last summer were exposed to a hybrid expressing the Cry3Bb1 protein as well as its corresponding isoline (not expressing the Cry3Bb1 protein), Gray said. Larvae obtained from three control colonies of Western corn rootworms also were used in the bioassays. The control larvae had never been exposed to corn rootworm Bt protein and were provided by the USDA North Central Agricultural Research Laboratory in Brookings, SD.

Gray said there continues to be some controversy regarding the most appropriate procedures (plant-based vs. diet-based bioassays) that should be used to confirm whether or not resistance to a Bt protein has developed by an insect population. Citing a University of Arizona study that defines key terms regarding resistance to Bt crops and pesticides, Gray offered the following definitions that are useful in communicating with producers who have experienced greater than expected levels of damage to rootworm Bt hybrids in their fields.They include:

  • “Resistance: genetically based decrease in susceptibility to a pesticide”
  • “Field-evolved resistance (= field-selected resistance): genetically based decrease in susceptibility to a pesticide in a population caused by exposure to the pesticide in the field”
  • “Practical resistance (= field resistance): field-evolved resistance that reduces pesticide efficacy and has practical consequences for pest control”

“It has become increasingly evident that some producers have experienced a loss of efficacy with some Bt hybrids in their fields in recent years,” Gray said. “To date, most of those fields have been in continuous corn production, and producers have not rotated traits. It’s also clear that ‘practical consequences’ have resulted due to the loss of efficacy associated with some Bt hybrids in problem fields.

“The primary consequence so far has been an escalation in the use of planting-time soil insecticides with Bt rootworm hybrids. This practice may hasten the onset of resistance evolution to Bt proteins as outlined in a paper published last year,” he added.

Other consequences of the evolution of practical resistance by the western corn rootworm has been the increased use of pyramided Bt hybrids, the use of seed blends as a primary refuge strategy, and a reduction in the size of the required refuge — from 20% to 5% for some products.

“The reduction in the refuge size remains troubling for many entomologists, especially in areas of the Corn Belt where resistance has been confirmed to one of the rootworm Bt proteins. Although a seed blend offers many advantages, including ensured compliance as well as improving the chances that Bt-susceptible and resistant adults will mate, increased selection pressure on the one effective Bt protein within a compromised pyramid, may be a primary consequence of a 5% refuge,” he said.

To date, four Bt rootworm proteins have been registered for use in the United States: Cry3Bb1, Cry34/35Ab1, mCry3A, and most recently eCry3.1Ab. Gray said that Aaron Gassmann (Iowa State University) and his colleagues recently published a paper in which they confirmed the field evolution of resistance to the mCry3A protein. In the same journal article, they also confirmed cross-resistance between Cry3Bb1 and mCry3A proteins.

“These findings are troubling from many perspectives. For instance, pyramided Bt hybrids that are used in areas of the Corn Belt where practical resistance to the Cry3Bb1 and mCry3A proteins is a reality, may in fact be relying to a great extent upon the efficacy of Cry34/35Ab1 or eCry3.1Ab to ensure adequate root protection — again, at reduced refuge size requirements (5%),” he said.

Last summer, Gray reported on the failure of some Bt hybrids (Cry3Bb1) to provide adequate root protection in rotated corn in Kankakee and Livingston counties. Spencer will conduct plant-based bioassays on the offspring reared from the adults collected from these fields. Results from these bioassays will be in later this year.

“If the results confirm resistance to the Cry3Bb1 protein, it seems clear that a segment of the Western corn rootworm population can now overcome rotation and this protein. With cross-resistance within this population to the mCry3A protein a possibility, we begin to see how diminished our IPM tool box is for this insect pest,” Gray explained.

“As I have done in the past, I urge producers to implement a long-term integrated pest management approach for corn rootworms. This includes the use of multiple tactics (over time, not all in the same season), such as: use of a more diverse crop rotation system, use of a non-Bt hybrid in conjunction with a planting-time soil insecticide, rotation of pyramided Bt hybrids, and consideration of an adult suppression program in heavily infested fields,” he said.

Leave a Reply

Crop Inputs Stories
Crop InputsPlatform Specialty Products To Acquire Arysta LifeScience
October 20, 2014
Once the acquisition is complete, Platform Specialty Products will combine Arysta LifeScience with previously acquired companies Agriphar and Chemtura Crop Solutions. Read More
MicronutrientsMicronutrients Going Macro
September 9, 2014
Between 2014’s fantastic growing conditions and a heightened awareness on plant nutrition, the major players in micronutrients are gearing up for another big year. Read More
FertilizerFall Fertility 2014: Forecasting Fertilizer Use
September 7, 2014
Great crops this year have tapped the soil, and fall work is definitely called for, but how challenging will that get? Read More
FungicidesSudden Death Syndrome, Brown Stem Rot Reported In Indiana Soybeans
September 3, 2014
Farmers and retailers should be watching for symptoms of these two diseases over the next few weeks as they are best managed through preventative methods. Read More
Top 100 Articles
CropLife 100Pinnacle Agriculture Acquires Minnesota Retailer
April 14, 2015
Pinnacle Agriculture Holdings, LLC, ranked No. 6 on the CropLife 100,  has successfully acquired Liebl Ag, LLC in Ada, MN.  Read More
CropLife 100CHS, Aurora Cooperative Complete Fertilizer Storage, Grain Shuttle Loading Facility
April 13, 2015
CHS Inc., the nation’s leading cooperative and ranked No. 5 on the CropLife 100, and Aurora Cooperative (ranked No. 21) Read More
CropLife 100GROWMARK Acquires Missouri Refined Fuels Terminal
April 2, 2015
Bloomington, IL-based GROWMARK and Magellan Pipeline Co. have entered into an agreement in which GROWMARK will acquire the refined fuels Read More
CropLife 100Wilbur-Ellis Acquires South Dakota Retailer
April 2, 2015
Wilbur-Ellis Co.’s Agribusiness Division, a recognized leader in precision agriculture technology and the distribution and marketing of plant protection, seed Read More
CropLife 100The McGregor Co. Closes Smith-Kem Acquisition
April 2, 2015
The McGregor Co. — ranked No. 16 on the CropLife 100 list of largest U.S. ag retailers — has completed Read More
CropLife 100BRANDT Commemorates National Ag Day
March 20, 2015
The Illinois agriculture community gathered at BRANDT global headquarters on March 18 to celebrate National Ag Day behind this year's theme Sustaining Future Generations. Read More
Latest News
West Central Sac City growers
StewardshipIowa Lawsuit Challenges Ag’s Water Quality Efforts
May 3, 2015
Nutrient problems in west-central Iowa’s water supply made national headlines in March when the Des Moines Water Works (DMWW) filed Read More
Tim Hassinger Dow AgroSciences President and CEO
Crop InputsDow AgroSciences: Always About Agriculture
May 2, 2015
When you consider their respective backgrounds, it’s little wonder why Dow AgroSciences and new President/CEO Tim Hassinger ended up together. Read More
Nozzle spray close-up
AdjuvantsSpray Drift Enters More Complex Era
May 1, 2015
Off-target movement of crop protection products has been a problem for decades. The issue got more contentious when glyphosate-tolerant crops Read More
Crop InputsTop 10 Twitter Pics For #Plant15
April 30, 2015
Growers and ag retailers are working feverishly to plant this year’s crop. Fortunately, many of them still have time to Read More
ManagementIowa Retailer Sticks Up For Agriculture and New Spray D…
April 30, 2015
Paul Schrimpf and Eric Sfiligoj talk about how one Iowa ag retailer is working to defend agricultural practices and an Read More
Dow AgroSciences Logo wall
Seed/BiotechNew Soybean Trait Agreement To Use Dow AgroSciencesR…
April 30, 2015
Dow AgroSciences LLC, a wholly owned subsidiary of The Dow Chemical Co., Arcadia Biosciences, Inc. and Bioceres, S.A. have formed an agreement Read More
Confluence of St. Croix and Mississippi Rivers in Minnesota
StewardshipAgricultural Runoff Among Causes Of Water Quality Issue…
April 30, 2015
A new report released April 29 by the Minnesota Pollution Control Agency provides additional evidence that agricultural and urban runoff Read More
EquipmentTop 30 IRON WORKS Cartoons Of All Time
April 29, 2015
When CropLife IRON first started publishing more than a decade ago, long-time Publisher Al Strohmaier decided to start a cartoon Read More
StewardshipCPS-Hillsboro Becomes First ResponsibleAg Certified Fac…
April 29, 2015
Unlike a race where the first finisher takes home a medal or blue ribbon, safety and regulatory compliance doesn’t often Read More
HerbicidesWeed Scientists Offer New Definition For ‘Superwe…
April 28, 2015
The Weed Science Society of America (WSSA) has joined with six sister organizations to recommend a new definition for superweed Read More
Crop InputsValent Announces “Relentless As You’ Contes…
April 28, 2015
Valent U.S.A. Corporation today announced the winners of its national “Relentless As You” contest, which recognized the relentless spirit of Read More
HerbicidesSyngenta’s Acuron Secures EPA Federal Approval
April 28, 2015
Growers looking to control difficult weeds like waterhemp, giant ragweed and Palmer amaranth will have access to Acuron corn herbicide Read More
FertilizerSimplot’s Gal-XeONE Technology Moves West
April 27, 2015
The J.R. Simplot Co. remains committed to creating customer value through technology. In 2013, Simplot purchased the Gal-XeONE controlled release Read More
Eric SfiligojThe Need To Defend Production Agriculture
April 27, 2015
Last week, I spent the better part of my time on the road visiting with ag retailers and market suppliers Read More
FertilizerStarter Fertilizers Show Value In Stressful Spring Cond…
April 27, 2015
From wet, cold conditions in the eastern Corn Belt to excessively dry, cool soils in the Plains states, spring field Read More
StewardshipTFI Announces Renewed Financial Commitment To Fertilize…
April 24, 2015
Today, The Fertilizer Institute’s (TFI) President Chris Jahn announced that TFI and over 100 partners will more than double existing Read More
Industry NewsMACA Names New Ambassador Coordinator
April 23, 2015
The Mid America CropLife Association (MACA) has named Michelle Kilper as its new Ambassador Coordinator. Michelle is a graduate of Read More
ManagementAg Retailer’s Role In Local Policy Making; Raising The …
April 23, 2015
CropLife’s Paul Schrimpf and Eric Sfiligoj review their recent travels, precision ag efforts in Washington, DC, and the role of Read More