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

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
HerbicidesScouting Key To Next Season’s Soybean Herbicide Program
August 12, 2014
When growing soybeans, growers need to think ahead to stay one step ahead of weeds. That means examining weed threats and evaluating which herbicides work best. Read More

Trending Articles

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
CropLife 100CHS To Build $3 Billion Fertilizer Plant In North Dakota
September 5, 2014
The fertilizer plant in Spiritwood will be the single largest investment in CHS history, as well as the single largest private investment project ever undertaken in North Dakota. Read More
EquipmentNew Holland Acquires Miller-St. Nazianz
September 3, 2014
The assets of Miller acquired as part of the transaction will become part of New Holland Agriculture, a CNH Industrial brand, building on a successful four-year partnership between the two companies. Read More
CropLife 100Pinnacle Acquires East Kansas Chemical
September 2, 2014
Ranked 82nd on the CropLife 100, East Kansas Chemical will operate as part of Pinnacle's Performance Agriculture brand. Read More
MAGIE 2014 ShowStopper
EquipmentJohn Deere Again Wins MAGIE ShowStopper Award
August 25, 2014
For the second consecutive year, John Deere was honored at the Midwest AG Industries Exposition (MAGIE) for its new R4045 sprayer. Read More
ManagementExpert To Discuss Farmland Value, Rent At Farm Science Review
August 18, 2014
While cropland values in Ohio increased in the past two years, they have remained flat in 2014, declining in some cases, according to an Ohio State University agricultural economist. Read More

Latest News

Equipment2014 Product Of The Year Voting
September 19, 2014
Many new products were introduced to the ag retail marketplace this year. From this group, CropLife IRON and its consulting partners have selected five finalists for the Product of the Year award. Please cast your vote today to help us determine the winner. Read More
Equipment2014 Farm Science Review Crowd Tops 2013 Show
September 19, 2014
The 52nd annual Ohio State University Farm Science Review welcomed more than 130,000 farmers, industry professionals, FFA students and agricultural enthusiasts during the three-day event. Read More
Seed/BiotechUSDA Approves Enlist Following Rigorous Review
September 18, 2014
Dow AgroSciences now awaits EPA registration of Enlist Duo herbicide, the companion herbicide to the Enlist traits, which is expected in the near future. Read More
BlendersYargus Appoints New Plant Manager
September 18, 2014
Steve Shaffer will direct and coordinate daily operations at the company’s Marshall, IL, manufacturing plant, where the Layco line of material handling equipment is produced. Read More
CropLife 100Pinnacle Acquires Kansas-Based Cedar Ridge Supply
September 16, 2014
Cedar Ridge Supply will operate as part of Pinnacle's Performance Agriculture brand. Read More
StewardshipSecretary Vilsack Highlights Innovative Conservation Ef…
September 15, 2014
Nearly $16 million in Conservation Innovation Grants (CIGs) will be awarded to 47 organizations to help develop cutting-edge ideas to accelerate innovation in private lands conservation. Read More
Seed/BiotechSyngenta Responds To Cargill Lawsuit
September 15, 2014
Syngenta believes that the lawsuit is without merit and strongly upholds the right of growers to have access to approved new technologies. Read More
Equipment2014 Farm Science Review Launches Mobile App
September 15, 2014
Smartphone and tablet users planning on attending the 2014 Farm Science Review can now download this year’s customized mobile application. Read More
CropLife 100Southern States Coop Grower Sets Georgia Soybean Yield …
September 15, 2014
Georgia farmer Randy Dowdy's soybeans yielded an astonishing 110.66 bushels per acre, crushing the previous record of 82 bushels-per-acre. Read More
NIMITZ Treated vs Untreated pepper plant
InsecticidesNIMITZ Nematicide Approved By EPA
September 12, 2014
NIMITZ is a novel, non-fumigant nematicide with simplified application features, user safety and an active ingredient with a unique mode of action. Read More
InsecticidesMarrone Bio Innovations Receives Patent For Chromobacte…
September 11, 2014
The patent is the first step for MBI in developing a commercially viable product to inhibit infestations of corn rootworm larvae across America and other regions. Read More
HerbicidesDow AgroSciences: Keeping The Pipeline Stocked
September 11, 2014
Dow AgroSciences is embracing product diversity to drive the company’s future. Read More
CropLife 100CHS Is Official Partner Of New St. Paul Ballpark
September 10, 2014
The new ballpark in St. Paul, MN, officially became CHS Field with Twin Cities-based CHS Inc. revealed as the naming rights partner. Read More
EquipmentHagie Honors Farming Stewardship Leaders
September 10, 2014
The Iowa Farm Environmental Leader award recognizes Iowa farmers as environmental leaders that are committed to healthy soils and improved water quality. Read More
Precision AgPlantBeat: Your Plants’ Pulse In The Palm Of Your Han…
September 10, 2014
A new agronomic monitoring and recommendation service from Phytech could rewrite the book on real-time plant health status monitoring. Read More
StewardshipCCAs Making Headway With 4R Program In Lake Erie Wester…
September 9, 2014
Certified Crop Advisers are implementing the 4R Nutrient Stewardship Certification program in Lake Erie's Western Basin to improve water quality. 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
Crop InputsFMC Announces Cheminova Takeover
September 8, 2014
FMC Corporation today announced that it has signed a definitive agreement to acquire Cheminova, a wholly owned subsidiary of Auriga Industries. Read More