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 100The Andersons Acquires South Dakota Plant Nutrient Manufacturer Kay-Flo
May 20, 2015
The Andersons, Inc., ranked No. 22 on the CropLife 100, has purchased Kay Flo Industries of North Sioux City, SD. “This Read More
CropLife 100North Central Farmers Elevator, Wheat Growers Unification Approved By Board, Still Awaits Member Approval
May 13, 2015
The Boards of Directors for North Central Farmers Elevator (NCFE) and Wheat Growers (WG) have voted to approve the Unification Read More
CropLife 100AgGateway’s Barcoding Initiative Progressing Nicely
May 8, 2015
According to legend (or Wikipedia), the first step towards modern bar codes came back in 1948, when Bernard Silver, a Read More
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
Latest News
ManagementA New Sprayer Company & UAV Research In The Spotlig…
May 21, 2015
CropLife’s Paul Schrimpf and Eric Sfiligoj talk about a Dutch sprayer manufacturer entering the U.S. with a super-sized entry and Read More
HerbicidesFirst U.S. Sale Of Enlist Duo Herbicide Made By Dow Agr…
May 21, 2015
Dow AgroSciences has recorded the first U.S. sale of Enlist Duo herbicide with Colex-D Technology. This marks the first commercial Read More
CropLife 100The Andersons Acquires South Dakota Plant Nutrient Manu…
May 20, 2015
The Andersons, Inc., ranked No. 22 on the CropLife 100, has purchased Kay Flo Industries of North Sioux City, SD. “This Read More
EquipmentNORAC Options Coming To TerraGator
May 19, 2015
Utilizing NORAC’s Standard Control technology, boom height control is now available for TerraGators with Airmax Precision 2 and Benson Booms. This Read More
Crop InputsHelena Introduces New Soil Health Product
May 19, 2015
Helena Chemical Co. is helping agricultural producers maximize yields and efficiency with the introduction of Liquid Chisel, a new product Read More
Stewardship4R Nutrient Management Planning Certification Now Avail…
May 19, 2015
The American Society of Agronomy (ASA) and the International Certified Crop Adviser (ICCA) program announce a new specialty certification in Read More
Environmental Defense Fund logo
Paul SchrimpfEnvironmental Defense Fund: Appreciating Partners
May 19, 2015
I WAS deep in the throes of preparation for the Commodity Classic meeting that took place this past February, trying Read More
WebinarsUpcoming Webinars
May 19, 2015
Register for one of our upcoming Webinars or access our archive of past Webinars to view recordings of presentations that may be of interest to you. Read More
Syngenta Sign
Seed/BiotechSyngenta Responds To Lawyer’s Victory Claim In Vi…
May 18, 2015
A plaintiff’s lawyer has issued a public statement claiming that damages have been awarded in the Agrisure Viptera corn lawsuits Read More
StewardshipCould Australian Water Trading Approach Fit In Californ…
May 18, 2015
Ten years of drought isn’t a good thing. It doesn’t help the bottom line of farmers or the health of Read More
SpreadersDutch Sprayer Manufacturer To Enter U.S. Market
May 18, 2015
Dutch self-propelled sprayer manufacturer Agrifac Machinery has announced intentions to enter the U.S. market with two models of sprayers available Read More
FertilizerTFI Weighs In On Fertilizer Rail Transport Bill
May 14, 2015
With today’s House Committee on Transportation and Infrastructure as a backdrop, The Fertilizer Institute (TFI) registered its support for policies Read More
ManagementA Visit To The 2015 Environmental Respect Spirit Award …
May 14, 2015
CropLife’s Paul Schrimpf and Eric Sfiligoj talk about a recent visit to the CPS Spirit winner in St. Stephen’s Church, Read More
StewardshipBayer Entomologist Issues Statement On Annual Honeybee …
May 13, 2015
Richard (Dick) Rogers, Principal Scientist / Entomologist, Bayer Bee Care Center for Bayer CropScience LP, today issued the following statement Read More
Crop InputsKansas State Researchers Announce Resistant Kochia Brea…
May 13, 2015
Kansas State University researchers say new research helps explain why an invasive weed is developing resistance to a well-known herbicide, Read More
RR2X soybeans surround untreated check (center)
HerbicidesUSDA Study: Glyphosate Application More Prevalent In So…
May 13, 2015
Glyphosate—known by many trade names, including Roundup—has been the most widely used pesticide in the United States since 2001. It Read More
AdjuvantsHelena Chemical Introduces New Drift Control Adjuvant J…
May 13, 2015
Helena Chemical Co. introduces Justified, an innovative drift control agent designed to improve the performance and precision of spray applications Read More
CropLife 100North Central Farmers Elevator, Wheat Growers Unificati…
May 13, 2015
The Boards of Directors for North Central Farmers Elevator (NCFE) and Wheat Growers (WG) have voted to approve the Unification Read More